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4
Organizing Science Education Around Core Concepts
In order to develop a deep understanding of scientific explanations of the natural world, students need sustained opportunities to work with and build on the concepts that support these explanations and to understand the connections between concepts. Yet many science curricula consist of disconnected topics, with each given equal priority. Too little attention is paid to how students’ understanding of a concept can be built on from grade to grade. While students are continually introduced to new concepts, unless those concepts connect to other related ideas, they will not build conceptual understanding in a meaningful way.
Research strongly suggests that a more effective approach to science learning and teaching is to teach and build on core concepts of science over a period of years rather than weeks or months. These core concepts offer an organizational structure for the learning of new facts, practices, and explanations, and they prepare students for deeper levels of scientific investigation and understanding in high school, college, and beyond.
Other ways have been proposed to organize science curriculum and instruction over extended periods of time, and it is important to distinguish between these other proposals and the teaching and building of core concepts. For example, the American Association for the Advancement of Science has proposed a set of themes—constancy and change, models, systems, and scale—that would extend across science curricula. These themes are much broader in scope than the core ideas, and they are not clearly rooted in science. The core concepts are science ideas that have been well tested and validated and are central to the disciplines. Examples of core concepts in science are the atomic-molecular theory of matter, evolutionary theory, cell theory, and Newtonian laws of force and motion—all of which are considered foundational ideas in science. Each integrates many different findings and is the source of coherence for many key
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concepts, principles, and even other theories in the discipline. Each guides new research and can be understood in progressively more complicated ways. Each enables creative links to be made between disciplines. For example, atomic-molecular analyses are important in physics, chemistry, biology, and geology. Biologists work with DNA molecules to understand patterns in genetic code and unravel the interrelations of species. Chemists seek to articulate the laws that govern interactions between molecules that result in newly formed or broken chemical bonds. And teams of multidisciplinary experts—including chemists and biologists—draw heavily on molecular science to develop drugs that attack unhealthy molecules (or cells) and leave others undisturbed.
Examples of Core Science Concepts
Atomic-molecular theory of matter
Evolutionary theory
Cell theory
Newtonian laws of force and motion
The proposed use of core concepts and learning progressions still requires significant additional research and development on the part of science educators, scientists, and education researchers. The science education community will need to identify core ideas, and specific learning progressions will need to be developed and tested extensively in classrooms.
Here we define learning progressions and offer an example of how learning progressions might be structured over the course of the K-8 school years. This is a dramatic departure from current classroom practice. Many educators and school systems are not in a position to pursue an immediate wholesale change to their science curricula. Accordingly, later in the chapter we reflect on the incremental steps that can be made right away at the classroom and the school levels.
Building on Core Concepts Over Time
Organizing science education around core concepts that provide a specific context for learning is a significant departure from typical classroom practice. Science educators must work cooperatively to define long-term goals for students that take into account the reality that students need opportunities to learn over multiple years to deepen their understanding of scientific concepts. Much thought will need to be given to how specific experiences along the K-8 grade span will accumulate and contribute to student learning and how to provide the kinds of support that teachers will need to accomplish this.
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The core concepts used in this practice would be dramatically fewer in number than those currently focused on or included in standards and curriculum documents. This would allow teachers and teacher educators to focus on building and deepening their own knowledge of a smaller number of critical science concepts. At the same time, a grade-level teacher would need to be concerned not only with the relevant “slice” of a given core idea taught in her particular grade, but also with the longer continuum of learning that K-8 students experience. Thus, teachers and science teacher educators (at the district, school, and college levels) would need to build structures and social processes to support the exchange of knowledge and information related to core concepts across grade levels.
Because core ideas are bound up in the practices of science, teachers would also need a solid foundation in science and excellent classroom skills to guide and extend students’ experiences. Again, a network of science educators would need to work together to ensure that the complex instructional practices described here are supported with systematic, sustained professional learning throughout teachers’ careers. An excellent curriculum built on core ideas is but one of many major shifts required.
At the same time that science teachers are identifying and promoting long-term goals and connections related to core concepts, they must also define shorter term goals for students that involve more immediate understanding. At each grade level, teachers will need to aim for teaching specific intermediate ideas, with an eye to how these will connect with and inform the more sophisticated concepts that students are building toward understanding. For example, later in this chapter we describe a K-2 level intermediate understanding of atomic-molecular theory that does not employ the language of “atoms,” “molecules,” or “theory.” Instead, it builds essential conceptual bases for students to learn atomic-molecular theory in progressively more complex ways over the years.
Although most schools and school systems maintain control over the science curriculum, in the short term, individuals and small groups of science educators may find that they have opportunities to organize instruction in their own classrooms in a way that will build students’ understanding of core ideas across the year. Gradually, as this approach is implemented in schools and districts, science curricula can be organized around a limited number of key scientific concepts that are linked over successive grades.
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Core Concepts in Relation to Standards and Benchmarks
In the 1990s, the K-12 subject matter communities, comprised of education researchers, curriculum developers, scientists, teacher educators, and teachers, developed frameworks to guide state and local authorities with curriculum development. These became the National Science Education Standards (NSES)1 and the Benchmarks for Science Literacy.2 In turn, local and state authorities developed standards, curricula, and assessments that were meant to align with the national standards.
The development of standards and benchmarks was an important step toward building and expressing shared values for K-12 science education. These standards succeeded in building common frameworks. While standards were marginally rooted in research on children’s learning and analyses of scientific practice, we now have a richer research base to inform science education and a better sense of the critical role this research should play.
Current national, state, and district standards do not provide an adequate basis for designing effective curriculum sequences, for several reasons. First, they contain too many topics. When the NSES were compared with curricula in countries that participated in the Third International Mathematics and Science Study, the NSES were found to call for much broader coverage of topics than those in high-achieving countries.3
Second, the NSES and benchmarks do not identify the most important topics in science learning. Comparisons of the NSES with curricula in other countries show that they provide comparatively little guidance for sequencing across grades. As we pursue a course of organizing curricula around core ideas, we need to ask ourselves questions that were not central to the development of the current standards. What areas of study are critical for students’ future learning? Which of these critical areas of scientific study can students explore in meaningful and increasingly complex ways across the K-8 grade span and beyond? Which areas of science can safely be deferred until high school or college? These are not easy questions, and answering them will require collective, sustained attention and focus among a number of stakeholders.
Finally, the NSES and benchmarks provide limited insight into how students’ participation in science practices can be integrated with their learning about scientific concepts; that is, they do not describe how an understanding of scientific concepts needs to be grounded in scientific practice. In addition, although the
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NSES and benchmarks recognize the importance of the first three strands of science learning, each strand is described separately, so the crucial issue of how the strands are interwoven and how they support each other is not addressed.
Although there is a solid research base that supports the premises of organizing science around core concepts, one should be mindful that few studies have examined children’s learning of core concepts over multiple years. So questions about what the optimal set of core concepts are, how they should be distributed and organized over the grades, and how to link together instruction across the grades are as yet unanswered. It is, however, very clear that future revisions to the national science standards—and the subsequent interpretation of those standards at the state and local levels and by curriculum developers—should dramatically reduce the number of topics of study and provide clear explanations of the knowledge and practices that can be developed from kindergarten through eighth grade.
Using Core Concepts to Build Learning Progressions
Research indicates that one of the best ways for students to learn the core concepts of science is to learn successively more sophisticated ways of thinking about these ideas over multiple years. These are known as “learning progressions.” Learning progressions can extend all the way from preschool to twelfth grade and beyond—indeed, people can continue learning about core science concepts their whole lives. If mastery of a core concept in science is the ultimate educational destination, learning progressions are the routes that can be taken to reach that destination.
Learning progressions for K-8 science are anchored at one end by the concepts and reasoning abilities that young children bring with them to school and at the other end by what eighth graders are expected to know about science. The most effective and appropriate concepts on which to build learning progressions are those that are central to a discipline of science, that are accessible to students in some form starting in kindergarten, and that have potential for sustained exploration across grades K-8. A well-designed learning progression will include the essential underlying ideas and principles necessary to understand a core science concept. Because learning progressions extend over multiple years, they prompt educators to think about how topics are presented at each grade level so that they build on and support each other.
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Learning progressions have many other potential benefits. They can draw on research about children’s learning in determining the scope and sequence of a curriculum. They can incorporate all four strands of scientific proficiency. Since they are organized around core concepts, they engage students with meaningful questions and investigations of the natural world. They suggest the most appropriate ages for introduction of core concepts. And they can suggest the most important tools and practices to assess understanding.
In this chapter, we’ll be examining a learning progression based on the atomic-molecular theory of matter. The idea that all matter is composed of atoms and molecules is a core scientific concept that all students should master. It allows for the integration of many different scientific findings and explains otherwise puzzling aspects of the physical world. It allows for links to be made between various scientific disciplines, including physics, chemistry, biology, and geology. We explore this learning progression to illustrate the intermediate levels of understanding achieved at various points throughout the K-8 curriculum and how this understanding is rooted in science and learning research. We intend for this to serve as an example that can be further elaborated, tested, and emulated in the service of developing learning progressions in other areas of study.
Some Benefits of Learning Progressions
They require serious thinking about the underlying concepts that need to be developed before a student can master a particular area of science.
They prompt educators to think about how topics are presented at each grade level so that they build on and support each other.
They can draw on research about children’s learning in determining the scope and sequence of a curriculum.
They can incorporate all four strands of scientific proficiency.
They engage students with meaningful questions and investigations of the natural world.
They suggest the most appropriate ages for introduction of core concepts.
They can suggest the most important tools and practices to assess understanding.
The learning progression in this chapter is divided into three grade bands—grades K-2, grades 3-5, and grades 6-84—with a case study at each grade band that focuses on one or more of the concepts covered as part of atomic-molecular theory. This learning progression was designed so that students can give progressively more sophisticated answers to the following questions:
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What are things made of, and how can we explain their properties?
What changes, and what remains the same, when things are transformed?
How do we know?
A well-designed learning progression on atomic-molecular theory won’t mention atoms and molecules in the earliest grades. The notion of atoms, chemical substances, and chemical change are complex ideas that take time to develop, test, expand, and revise. These ideas are too advanced for most young children, although some may have heard about atoms and molecules and may use these terms or ask questions about them. The point is to emphasize the goal of understanding concepts, which is very different than merely memorizing vocabulary or definitions. By not emphasizing technical terms in the early grades, the teacher avoids sending the counterproductive message to students that science is about memorizing terms and definitions for phenomena that they fundamentally don’t understand.
Even in the later years of elementary school, students may not be ready for the idea that all matter is composed of atoms and molecules. They first need to develop a sound macroscopic understanding of matter. In general, one of the most difficult transitions children must make during the K-8 years is linking macro-level processes with micro-level phenomena. For example, elementary school students may think that, at a molecular level, wood will look like tiny pieces of wood, rather than consisting of molecules. It takes several years for students to work out the subtleties of understanding the basic constituents of matter (atoms and molecules) and how they combine to create larger units.
It is important to keep in mind that a learning progression is not a lockstep sequence. Different classrooms, and even different students within the same classroom, can follow different pathways in coming to understand core science concepts. There are many ways to learn that all matter is composed of atoms and molecules.
The following case study involves a classroom of kindergartners who are investigating the idea that different objects are made out of different materials, that there is a difference between what an object is used for (its function) and what it is made of (its material kind), and that these different materials have properties that can be discussed, examined, and described.
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Science Class THE MYSTERY BOX (GRADES K-2)5
“Are you ready to run a Mystery Box investigation with me?” Shawna Winter asked as her 22 kindergartners gathered around her. The classroom erupted into cheers. “Look at all these different eating utensils I’ve brought from home.” She pointed to two identical sets of spoons and forks made of three different materials. Each set was lined up in a row in front of a wooden chest a little bigger than a toaster. The box was latched shut with a heavy lock, and next to the box was a key tied to a long ribbon (see Figures 4-1 and 4-2).
“One set of these utensils is going to be mine, and the other set is going to be yours,” Ms. Winter said. She quickly established with the children the names of each of the utensils and the material it was made of. “So,” she summed up, “we have a plastic spoon, a wooden spoon, and a metal spoon, as well as a plastic fork, a wooden fork, a metal fork.”
“Now I’m going to take my whole set away,” she said, scooping up one row of the spoons and forks and tossing them into a bag. “Then I’m going to take one item—just one—from my set and put it into the Mystery Box. Close your eyes. No peeking!” All 22 kindergartners gleefully covered their eyes.
Ms. Winter turned her back to the kids, unlocked the Mystery Box, selected an item from her bag of utensils, and locked it inside the box with the key. The students’ set of six items—forks and spoons—remained lined up in front of the Mystery Box.
“Now open your eyes,” she said. “Inside the Mystery Box is one thing taken from my set of objects, which is just like your set. And here’s the amazing thing. You’re going to figure out what is inside the Mystery Box just by asking me questions.” Then, very dramatically, Ms. Winter uttered the words she always used to start the Mystery Box
FIGURE 4-1 The Mystery Box.
FIGURE 4-2 Eating utensils used with the Mystery Box.
game. “If you ask me a question about what’s inside the Mystery Box, I will tell you the truth.”
“I know,” said Maya. “Is it the plastic spoon?”
“That is a very good question, Maya. Do you know why it’s a good question? It’s a good question because … it’s not the plastic spoon.” Several kids giggled; a few sighed with disappointment.
“So Maya’s question has taught us something important,” Ms. Winter said. “Whatever is inside the box, it is not a plastic spoon. So that means we don’t need this one here anymore.” She picked up the plastic spoon from the students’ set of utensils and put it on the table, out of sight.
Ms. Winter reached into a cup of Popsicle sticks that had all of the children’s names written on them, which she used to ensure that each child had an equal chance of getting a turn. The stick she pulled from the cup had “Carlos” written on it.
“Carlos, what question do you want to ask?” Carlos was new to the classroom, having moved to
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the United States from Central America just a few weeks before. Carlos said nothing for several seconds. Ms. Winter and the children waited. Then Carlos said, “Tenedor, um, fork!”
Marisa, who was sitting next to Carlos, piped up. “He’s supposed to ask it as a question, right?”
“Marisa’s right,” said Ms. Winter. “You’re asking if there’s a fork inside our Mystery Box, Carlos, is that right?” Carlos nodded. “Can you say it as a question?”
“Is it a fork?” Carlos asked.
“Is it a fork?, Carlos wants to know,” said Ms. Winter. “That’s another good question, because what is in the Mystery Box … is not a fork.” The children laughed and clapped. “And because it’s not a fork, what have we learned?” Ms. Winter picked up the plastic fork, the wooden fork, and the metal fork.
“We don’t need them,” two children said.
“Right. Because we know it’s not a fork in our box, we can get rid of every single fork. It can’t be one of these.” Ms. Winter put the three forks out of sight.
“Hey, I just noticed something interesting,” said Ms. Winter. “With Maya’s question we got rid of one thing, the plastic spoon. With Carlos’s question, we got rid of three things, all three forks. Can anyone figure out why that is?” No one said anything. Ms. Winter waited.
Finally, Kelly, who tended not to talk much in the large group, raised her hand. “Carlos asked about all of the forks, and Maya just asked about the plastic one, just the plastic spoon.”
“Wow! Did anyone hear what Kelly said?”
Lots of hands went up.
“Does anyone think they can put what Kelly said in their own words? Yes, James?”
“She said Carlos asked his question about all the forks. Maya asked about only one spoon—the plastic spoon. It’s like we got three answers with one question.”
“Is that what you were saying, Kelly?”
Kelly nodded.
“Wow, you guys are really thinking today. I can see smoke coming out of your ears. Let’s see who’s next. Lassandra?”
“It has to be a spoon,” several children called out.
“Ah, but which spoon? What is the spoon made of?” Ms. Winter asked. “Lassandra?”
“Is it the wooden spoon?”
“That’s a very good question. Do you know why? Because, I’m telling you the truth, it is the wooden spoon.” The kids squealed with delight. Ms. Winter reached for the key. “So you think there’s going to be a wooden spoon in there? How certain are you?”
“A billion percent,” called out Jason. Slowly and dramatically Ms. Winter removed the lock and opened the doors of the Mystery Box, revealing—“Ta dah!”—the wooden spoon inside. “Congratulations,” Ms. Winter said. “Just by asking questions, without being able to see inside, you’ve discovered what’s in the Mystery Box.” Ms. Winter’s 22 kindergartners broke into applause.
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The Mystery Box activity may seem a long way from the kinds of scientific investigations children will do in later grades relating to the atomic-molecular structure of matter, but it actually has some important similarities. Students are using their reasoning abilities to draw inferences about something they can’t see. They are thinking about how to ask questions and how to learn from other people’s questions. They are learning that different kinds of questions can produce different amounts of information. Perhaps most importantly, they are learning that getting the right answer isn’t the only thing that matters in a scientific investigation. Negative evidence can be very useful.
While the Mystery Box activity doesn’t directly address the atomic structure of matter, it enables Ms. Winter’s kindergartners to practice making a distinction that will be essential in their understanding of matter. They are separating the use or type of an object (spoon or fork) from what it’s made of, or its “material kind” (plastic, wood, or metal). This may seem to be a simple task—indeed, it’s something that children generally master before they begin school. But they have to make this distinction clearly before they can learn about the detailed properties and microscopic composition of matter.
Science learning can be very effective when it is grounded in a task that supports multiple predictions, explanations, or positions. In such a setting, children have reasons to “argue” (to agree and disagree) and to back up their positions with evidence. These rich tasks involve the students in actual scientific investigations but require support and guidance from the teacher.
For example, the Mystery Box activity is a focused, teacher-guided activity, but the children are playing active roles, reasoning and theorizing. They are listening hard to one another and building on one another’s ideas. Ms. Winter is also actively involved, pressing them to clarify and explain their ideas to one another. The activity involves a whole-group discussion in which everyone takes
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part and has equal access to everyone else’s thinking, with help from Ms. Winter to keep the discussion on track. In addition, the Mystery Box activity can be played in many different ways and can be used to classify many different kinds of objects over the course of the school year. This activity can help students become thoughtful and logical questioners and data analysts.
The Mystery Box is an activity that supports logical or deductive reasoning practices. The implicit reasoning of the students as they play is as follows: We know that what’s in the Mystery Box is not a plastic spoon. We also know it’s not the plastic fork, the metal fork, or the wooden fork. Therefore, we have figured out that what’s in the Mystery Box must be a metal spoon or a wooden spoon, because they’re the only choices left.
In contrast, the proposed measurement activity in Ms. Martinez’s kindergarten class (Chapter 1) would be considered an “empirical investigation.” In that case, the students tested a prediction: “Measuring with shoes on would make a difference in measurement.” They would need to examine evidence to suggest a pattern and then interpret the pattern to decide if their prediction was correct or not. They would thus be arranging the world (selecting, lining up, and measuring shoes) in order to learn something about it. They would have to collect measurement data, organize the data in some way, and then decide, based on their evidence, whether wearing shoes made a difference or not. The data might prove difficult to interpret (most shoes are the same but a few are different), and the students might never be as certain of the right answer as they are with the Mystery Box activity. Generalizations about the empirical world are never certain. You cannot “prove” generalized conclusions via observation. Moderating uncertainty is central to scientific thinking. Unlike proof in mathematics, there is no absolute certainty in science.
The skills the students are learning in the Mystery Box activity—making sense of, categorizing, and reasoning with available information—are key to asking good questions and formulating good hypotheses. And of course the students are also learning to participate in discussions with peers. That is, they are learning the norms of participation in science and how to handle uncertainty together.
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Teaching the Atomic-Molecular Theory at the Middle School Level
In grades 6-8, building on robust learning experiences in the lower grades, students are ready to make a fundamental conceptual leap. They are ready to explain a host of new phenomena, and to reexplain phenomena they are already familiar with, using a new understanding of atoms and molecules. This new understanding will enable them to distinguish between elements and compounds. They can begin to recognize other considerations in tracking the identity of materials over time, including the possibility of chemical change. Some transformations involve chemical change (e.g., burning, rusting) in which new substances, as indicated by their different properties, are created. In other changes (e.g., changes of state, thermal expansion), materials may change appearance but the substances in them stay the same. Students can describe and explain the behavior of air or other gases. In general, they come to appreciate the explanatory power of assuming that matter is particulate in nature rather than continuous.
The learning progression proposes that, during these grades, students can be introduced to the following core tenets of atomic-molecular theory:
Matter exists in three general phases—solid, liquid, and gas—that vary in their properties.
Materials have characteristic properties, such as density, boiling point, and melting point.
Density is quantified as mass/volume.
At the microscopic level:
There are more than 100 different kinds of atoms; each kind has distinctive properties, including its mass and the ways it combines with other atoms or molecules.
Each atom takes up space, has mass, and is in constant motion.
Atoms can be joined (in different proportions) to form molecules or networks—a process that involves forming chemical bonds between atoms.
Molecules have characteristic properties different from the atoms of which they are composed.
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These are not simply facts to be memorized. These are complex concepts that students need to develop through engagement with the natural world, through drawing on their previous experiences and existing knowledge, and through the use of models and representations as thinking tools. Students should practice using these ideas in cycles of building and testing models in a wide range of specific situations.
At this grade band, students can begin to ask the questions: What is the nature of matter and the properties of matter on a very small scale? Is there some fundamental set of materials from which other materials are composed? How can the macroscopically observable properties of objects and materials be explained in terms of these assumptions?
In addition, armed with new insight provided by their knowledge of the existence of atoms and molecules, they can conceptually distinguish between elements (substances composed of just one kind of atom) and compounds (substances composed of clusters of different atoms bonded together in molecules). They can also begin to imagine more possibilities that need to be considered in tracking the identity of materials over time, including the possibility of chemical change.
Students have to be able to grasp the concept that if matter were repeatedly divided in half until it was too small to see, some matter would still exist—it wouldn’t cease to exist simply because it was no longer visible. Research has shown that as students move from thinking about matter in terms of commonsense perceptual properties (something one can see, feel, or touch) to defining it as something that takes up space and has weight, they are increasingly comfortable making these kinds of assumptions.
This is one example of the ways in which the framework that students developed in the earlier primary and elementary grades prepares them for more advanced theorizing at the middle school level. Middle school science students must conjecture about and represent what matter is like at a level that they can't see, make inferences about what follows from different assumptions, and evaluate the conjecture based on how well it fits with a pattern of results.
Research has shown that middle school students are able to discuss these issues with enthusiasm, especially when different models for puzzling phenomena are implemented on a computer and they must judge which models embody the facts. This approach led students who had relevant macroscopic understanding of matter to see the discretely spaced particle model as a better explanation than alternatives (e.g., continuous models and tightly packed particle models). Class discussions allowed students to establish more explicit rules for evaluating
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models: models were evaluated on the basis of their consistency with an entire pattern of results and their capacity to explain how the results occurred, rather than on the basis of a match with surface appearance. In this way, discussions of these simulations were used to help them build important metacognitive understanding of an explanatory model.
Describing and explaining the behavior of air or other gases provide still more fertile ground for demonstrating the concept that matter is fundamentally particulate rather than continuous. Of course, these investigations are effective only if students understand that gases are material, an idea that the proposed learning progression recommends they begin to investigate at the grades 3-5 level.
At the same time, coming to understand the behavior of gases in particulate terms should help consolidate student understanding that gas is matter and enable them to visualize the unseen behavior of gases. In other words, developing macroscopic and atomic-molecular conceptions can be mutually supportive. Direct support for this assumption was provided in a large-scale teaching study with urban sixth-grade students that compared the effectiveness of two curriculum units.9 One unit focused more exclusively on teaching core elements of the atomic-molecular theory, without addressing student misconceptions about matter at a macroscopic level. The other included more direct teaching of relevant macroscopic and microscopic concepts and talked more thoroughly about how properties of invisible molecules are associated with properties of observable substances and physical changes. The latter unit led to a much greater change in understanding phenomena at both macroscopic and molecular levels. Thus, sequencing instructional goals to reflect findings on student learning has important implications for how children make sense of science instruction.
Instruction that is focused on building core ideas is especially effective when students are regularly involved in classroom debates and discussion about essential ideas and alternative theories. Classroom debate and discussion make scientific experiments more meaningful and informative. Thus, building an understanding of atomic-molecular theory must also involve engaging students in cycles of modeling, testing, and revising models that describe a wide range of situations, such as explaining the different properties of solids, liquids, and gases, the thermal expansion of solids, liquids, or gases, changes of state, dissolving, and the transmission of smells.
Students engage in these types of discussions and investigations in the following case study.
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Science Class THE NATURE OF GASES (GRADES 6-8)
Over the past 10 years, the Investigators Club (I-Club) has sought to bridge what students already know about science and what they learn about science in school. The I-Club has been used in a variety of after-school and in-school settings. In its original design, the I-Club is an after-school program, meeting three times a week with students from a wide range of cultural and linguistic backgrounds, predominantly students from low-income families who are struggling or failing in school. It has since been expanded to include an in-school program in middle schools, as well as a prekindergarten curriculum. The following case involves 25 seventh- and eighth-grade students participating in an I-Club after-school program.
Richard Sohmer directs the Investigators Club program, which meets for 15 weeks each school term. There are no special tests or grade requirements for participating in the program, but students in the program have to commit to attending regularly, be respectful of one another, and work hard “to discover, practice, and acquire the skills of scientific investigation.”
Mr. Sohmer’s students were investigating air pressure and the nature of gases and were about midway through their investigation. Prior to this time, the students had begun learning about balanced and unbalanced forces.
In order to demonstrate concepts related to balanced and unbalanced forces, Mr. Sohmer had had two students stand on either side of him and push him hard but with equal force. Despite their efforts, he hadn’t moved. He had then instructed the student on his left, at the count of three, to take a step back, while the student on his right kept pushing. The result was that Mr. Sohmer had stumbled to the left, nearly falling down.
The demonstration had generated a discussion about how objects that were stationary had forces acting on them, but that these were balanced forces. The students had also explored the difference among the three phases of matter: solid, liquid, and gas. They had investigated how phases of matter stem from the interaction of molecular speed and intermolecular attraction.
It was at this point in their investigation that Mr. Sohmer introduced the students to a number of demonstrations, all of which involved everyday materials that the students were familiar with and which they could take home and share with their families. With each demonstration, the students predicted what would happen or attempted to explain what had caused the demonstration to work the way it did.
Over the years, he had found it difficult to disabuse his students of the notion of suction and vacuums as useful explanatory devices. Even though his students knew that air molecules don’t stick together and can’t hook onto anything and therefore can’t pull anything, they routinely invoked the idea of suction. To help his students adjust their view of how air pressure worked, Mr. Sohmer came up with an analogy, a narrative form of the ideal gas law, that he called the “Air Puppies” story.
Mr. Sohmer drew a large rectangle on the blackboard. He told his students to pretend that they were looking down at a large room.
“In this room is a special wall that divides the room into two parts. The wall is on roller blades, the kind with really good wheels, so it’s practically frictionless.”
Mr. Sohmer drew a line down the middle and showed the roller blades in red. He said: “The wall can move easily, to the right or left, if something touches it. So if I were standing on the left side of
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FIGURE 4-5 Mr. Sohmer’s wall-on-wheels.
the wall, and—by accident—I leaned against it, what would happen to the wall?” (See Figure 4-5.)
“It’ll move over there—it’s gonna move to the right!”
“True. And it’s going to keep on moving to the right until—remember, these are frictionless wheels—until it bounces off the end of the room, and comes back the other way.”
Then Mr. Sohmer told the story of the Air Puppies.
“Imagine that Air Puppies represent air molecules. Think about how newborn puppies bumble around constantly, mindlessly, with no intentions at all. They move around constantly, in every direction, like air molecules, without thinking, wanting, planning, or choosing to do anything.”
“Do Air Puppies breathe air like real puppies?” one of the students asked.
Mr. Sohmer responded by introducing a discussion about models and how they are never exactly the same as the thing they represent. Students volunteered examples: Model airplanes don’t fly. Maps don’t include the potholes that are on some roads. A menu doesn’t taste like the food it describes.
“Different models highlight different things,” he explained. “They’re useful in different ways. They make some things visible and other things invisible.”
This kind of discussion about the advantages and limitations of different models helped the students understand how scientific knowledge is constructed and how central models are in the construction of that knowledge. The Air Puppies are the bumbling (mindless) agents in a modifiable drama with a particular setting (always including two rooms separated by a moveable wall-on-wheels). The necessary result of the Air Puppies’ incessant, unintentional bumbling is a completely understandable, completely predictable, and thoroughly lawful effect—that is, the wall moves as it must, given the Air Puppies’ opposing impacts on both sides.
Mr. Sohmer continued the Air Puppies story. In his first version, the two rooms on either side of the wall-on-wheels each contain an equal number of identical Air Puppies mindlessly bumbling around and bumping into the walls and each other. The wall-on-wheels moves whenever a puppy bumps into it (see Figure 4-6).
FIGURE 4-6 The view from above at the beginning of the Air Puppies story showing an equal number and kind of Air Puppies on each side of the wall.
“So what will happen to the wall?”
“It’ll stay in the same place,” a number of students called out. With the aid of a QuickTime movie of an interactive physics animation, Mr. Sohmer demonstrated how the scenario in Figure 4-7 was set in motion. The wall stayed in approximately the same place, oscillating about the centerline (Figure 4-7).
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FIGURE 4-7 With an equal number and kind of Air Puppies on each side, the wall-on-wheels is continually bumped from side to side.
Mr. Sohmer continued with a variation on this basic story:
“What will happen to the wall if we have 25 Air Puppies on the left side and 10 Air Puppies on the right side?” Mr. Sohmer asked. He drew a diagram on the board (Figure 4-8).
“Point which way the wall will go.”
Everyone pointed to the right. “But it wouldn’t go all the way over,” Jennifer noted. “It would go about three-quarters of the way and then the puppies on the other side would be getting squished.”
“Wouldn’t the wall keep moving back and forth, just a bit, because the puppies on the right side would still be moving and hitting the wall?” Raul asked.
FIGURE 4-8 Divided room with 25 Air Puppies on the left side and 10 on the right side.
“Great! You’re starting to see how this model works!” Mr. Sohmer said. “As the 10 puppies on the right get more and more squished into less and less space, they’re going to get bounced more, and move faster and faster, and hit the wall more and more times. At the same time, the 25 puppies on the other side will still be bumbling around—but as their room expands each of the 25 puppies has, on average, farther to go before running into and bouncing off something. There will be more and more time between hits against the wall—they’ll be hitting the wall less often. The wall will move pretty far over to the right, then get pushed back some, to the left, and so on, ending up by shimmying back and forth around a point well to the right of the original centerline.”
Mr. Sohmer had another QuickTime video that showed exactly what would happen in this 25-to-10 situation. When he projected it from his computer onto the wall, the students watched the wall be driven to the right until a new equilibrium of puppy hits was established.
“Let me ask you one more thing,” said Mr. Sohmer. “When the wall moved over to the right, how did that happen? Was it due to suction?”
A chorus of voices called out, “No, the puppies on the other side pushed it over!”
Mr. Sohmer continued the discussion with another variation.
“What if we start out with the same number of Air Puppies on both sides of the wall, but the puppies on the left, the red puppies, are more active. They are excited and running fast, fast, fast, while the puppies on the right, the blue puppies, are just moving around at a normal, unexcited pace. What do you think is going to happen to the wall?”
“The fast puppies are gonna bump into the wall faster and more times and harder, so it’s gonna be pushed away, towards the slow puppies,” Sandra answered.
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Mr. Sohmer showed another QuickTime video, with the red Air Puppies moving much faster than the blue Air Puppies.
“This is a nifty picture definition of what heat is. The red Air Puppies are pounding on everything much more than the blue Air Puppies are—so we could say they are hot, and the blue puppies are cold. But as long as the blue puppies are moving at all—and they always will be—they will have heat energy. Even ice has heat!”
Mr. Sohmer added another variation to the story. “How about if we had our regular situation, with 100 puppies on one side and 100 puppies on the other, the same amount of excitement activity on both sides, but we make the room on the right bigger. What would happen to the wall then?”
“The wall’s going to move to the right,” Pedro said.
“Why do you think that?” asked Mr. Sohmer. “What’s making the wall move? Is it getting sucked over?”
“No, it’s getting pushed. There’s more space on the right, so the puppies bop around the same, but they don’t hit the wall as often.”
Mr. Sohmer then added another aspect to the problem by asking students to imagine what would happen when each room had an equal number of Air Puppies, but the room on the right had an open door (see Figure 4-9). The students reasoned that as Air Puppies escaped from the open door on the right, the wall would move to the right, resulting in the room on the right getting smaller and the room on the left getting bigger.
“What if you close the door after a lot of Air Puppies have already escaped from the right side?” Gina asked. “There’s going to be lots of space, and lots of puppies, on the left side, and then the wall between them, and then only a little teeny space over on the right side with hardly any puppies. But can the wall just destroy the puppies on the right?”
“No, they won’t be destroyed,” Mr. Sohmer said. “They’ll still be there, still be bumbling and bouncing around.”
“Then it seems like at some point, after a long time, the wall is going to come to some kind of balance point. It’s going to be somewhere way over on the right side, but it’s gonna eventually stop.”
“If the wall stops moving, does that mean there’s no more pressure, no more puppy hits per area?” asked Mr. Sohmer.
“No,” Gina said. “I think I get it. If the wall’s not moving, it just means that there’s the same number of hits on both sides, or equal pushes, or equal forces. Like when you had two guys pushing you the same on both sides and you didn’t move. So I guess you were like the wall!”
FIGURE 4-9 As Air Puppies in the right room bumble randomly out the open door, there are fewer and fewer Air Puppy impacts on the wall from the right. Increasingly unopposed Air Puppy impacts from the left push the wall to the right.
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“Truth!” Mr. Sohmer declaimed. Laughter and a buzz of speculation ensued about the other air pressure demonstrations the class had done.
“Okay all, so that’s the Air Puppies story,” Mr. Sohmer said. “With that story, you can see into a ton of interesting phenomena, explain to your parents how vacuum cleaners really work! But in order to know that you really understand the story, you have to be able to explain it to someone else. So I’d like you all to go home and explain it to someone there—a brother, a sister, a parent, a grandparent whoever is at home. And also explain one of the demos we did in class.”
Mr. Sohmer reminded the class that the Air Puppies story was a new tool, and that it was often difficult at first to use any new tool. He had his students each choose one of the air pressure demonstrations they had done and explain it to the group. The goal, Mr. Sohmer said, was to explain things clearly enough so that even a person who could only hear and not see them presenting could still understand what they were saying. The students in the audience listened to the explanations and made suggestions for how they could be explained more clearly or completely. Each presenter had as many chances as needed to revise their presentation, until everyone in the group was satisfied.
After a few weeks of practice in small groups using the Air Puppies model in many different situations, each group selected a demonstration and worked hard to develop a thorough, compelling, and cogent explanation of all the causal forces at work. These were eventually put on posters and presented in a schoolwide after-school celebration. The I-Club students also published a bimonthly Investigators Club newsletter, detailing their work and describing interesting physics demonstrations that could be done at home. Discussions of the demonstrations were written up in an issue. I-Club students developed teaching texts that were used to teach younger students and archived in the school library. They presented their work to adults in the community and participated in science fairs.
Many of the I-Club students were reluctant, struggling writers in school, and most read far below grade level. Nonetheless, every one of them decided that they wanted to prepare teaching texts. Of the 25 students, 23 voluntarily entered their school science fair, most of them doing physics projects that revolved around the power of air pressure. And 13 students were among their school winners and went on to the citywide competition.
In spite of the fact that they said they “hated to write in school,” the I-Club kids put an enormous effort into preparing science fair or teaching texts, writing as “experts” rather than as students. They worked in teams of four, adding elaborate photographs and diagrams, formatting their texts on the computer, soliciting comments from other groups, and drafting and revising.
These tasks motivated the students to take their thinking and their presentation of their ideas (in writing and orally) to a higher level. Sandra, one of the I-Club students, put it well when she said, “In school, they just give you a book. It’s boring. But in the I-Club, we really get to explain things, down to the very core of the problem. That’s why we did so well in the science fair.”
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The Benefits of Focusing on Core Concepts and Learning Progressions
As the cases in this chapter suggest, it takes considerable time and effort to introduce students to ideas about atomic-molecular theory in a meaningful manner. It is important to take that time at the middle school level for several reasons.
First, understanding atomic-molecular theory opens up many productive new avenues for investigating matter. For example, it introduces the concept of chemical change, which research suggests is not really accessible to students with only macroscopic criteria for identifying substances.
Understanding atomic-molecular theory also helps students more clearly understand what substances stay the same and what substances change during the water cycle. In addition, many important topics across the sciences—osmosis and diffusion, photosynthesis, digestion, decay, ecological matter cycling, the water cycle, the rock cycle—depend on an understanding of atomic-molecular theory.
Finally, atomic-molecular theory gives students an opportunity to begin developing an understanding of and respect for the intellectual work and experimentation needed to formulate successful scientific theories.
In current practice, atomic-molecular theory is often presented to students without careful attention to how their ideas develop through instruction or how to help them link science with their emergent ideas and relevant everyday experiences. As a result, as research makes clear, the majority of students fail to internalize the core assumptions of atomic-molecular theory, and they are unable to understand such important ideas as chemical change. Perhaps more importantly, students are not given the opportunity to recognize the standards that a scientific theory is built on, how it is formed, and why it cannot be challenged by other theories that do not meet the same rigorous epistemological standards. Without an understanding of those epistemological standards, students will not know the grounds on which they should test and believe scientific arguments.
Learning progressions are a promising way to design and organize science learning. Recognizing this, teams of educators and researchers are actively developing learning progressions with support from the National Science Foundation and other sponsors. For now, fully developed, well-tested learning progressions that are ready for broad application will have to wait. But that does not mean
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that science educators can’t use aspects of this work now. In fact, it is important for science educators to begin to consider how learning progressions might be used in their own schools and classrooms and how learning progressions might affect their current teaching practices. The effectiveness of learning progressions is dependent on committed and capable implementation, and they will benefit from the experience and feedback of early adopters who can also play an active role in refining the practice.
In order for productive science learning to take place, students and teachers need to have a clear idea of major conceptual goals. We’ve proposed a frame for thinking about K-8 goals, but shorter term goals can also be set for a four- to six-week unit or over a year of instruction. Science educators can begin to reflect on their curricular goals, identifying and focusing on those that are most scientifically powerful and fundamental.
Meaningful science learning takes time, and learners need repeated, varied opportunities to encounter and grapple with ideas. Identifying core ideas means making hard decisions about “coverage” and will require that a curriculum be pared down and significantly focused. For this reason, it is advisable to begin on a small scale. A group of teachers at a given grade level, for example, might begin with a single unit of study, one that they feel comfortable with; perhaps the unit they feel is the strongest at their grade. They will need to give themselves ample time to identify meaningful problems, figure out how best to sequence the unit, and plan lessons that will provide students with the skills they need to do the science involved. Beginning this effort a year in advance of trying to enact changes to the curriculum should allow time for adequate teacher learning and planning.
Whether at the state, district, school, or individual classroom level, as educators take up learning progressions, it is important to treat them as a research and development initiative. As such, educators will require support in order to break from current practice and embrace new ideas. They will require feedback on the quality of the changes they enact as well as student learning outcomes.
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For Further Reading
Lehrer, R., Catley, K., and Reiser, B. (2004). Tracing a trajectory for developing understanding of evolution. Invited paper for the National Research Council Committee on Test Design for K-12 Science Achievement. Available: http://www7.nationalacademies.org/bota/Evolution.pdf.
National Research Council. (2007). Learning progressions. Chapter 8 in Committee on Science Learning, Kindergarten Through Eighth Grade, Taking science to school: Learning and teaching science in grades K-8 (pp. 211-250). R.A. Duschl, H.A. Schweingruber, and A.W. Shouse (Eds.). Center for Education, Division of Behavioral and Social Sciences and Education. Washington, DC: The National Academies Press.
Schmidt, W., Wang, H., and McKnight, C. (2005). Curriculum coherence: An examination of U.S. mathematics and science content standards from an international perspective. Journal of Curriculum Studies, 37, 525-559.
Smith, C., Wiser, M., Anderson, C.A., Krajick, J., and Coppola, B. (2004). Implications of research on children’s learning for assessment: Matter and atomic molecular theory. Paper commissioned by the National Academies Committee on Test Design for K-12 Science Achievement. Available: http://www7.nationalacademies.org/bota/Big%20Idea%20Team_%20AMT.pdf.