The Insect and the Spider

Titles in this example emphasize some of the components of the assessment process. In the vision of science education described in the Standards, teaching often cannot be distinguished from assessment. In this example, Ms. M. uses information from observations of student work and discussion to change classroom practice to improve student understanding of complex ideas. She has a repertoire of analogies, questions, and examples that she has developed and uses when needed. The students develop answers to questions about an analogy using written and diagrammatic representations. The administrator recognizes that teachers make plans but adapt them and provided Ms. M. with an opportunity to explain the reasoning supporting her decision.

[This example highlights some elements of Teaching Standard A and B; Assessment Standard A, 5-8 Content Standard B, and Program Standard F.]

SCIENCE CONTENT: The 5-8 Physical Science Content Standard includes an understanding of motions and forces. One of the supporting ideas is that the motion of an object can be described by the change in its position with time.

ASSESSMENT ACTIVITY: Students respond to questions about frames of reference with extended written responses and diagrams.

ASSESSMENT TYPE: This is an individual extended response exercise embedded in teaching.

ASSESSMENT PURPOSE: The teacher uses the information from this activity to improve the lesson.

DATA: Students' written responses.
Teacher's observations.

CONTEXT: A seventh-grade class is studying the motion of objects. One student, describing his idea about motion and forces, points to a book on the desk and says "right now the book is not moving." A second student interrupts, "Oh, yes it is. The book is on the desk, the desk is on the floor, the floor is a part of the building, the building is sitting on the Earth, the Earth is rotating on its axis and revolving around the Sun, and the whole solar system is moving through the Milky Way." The second student sits back with a self-satisfied smile on her face. All discussion ceases.

Ms. M. signals time and poses the following questions to the class. Imagine an insect and a spider on a lily pad floating down a stream. The spider is walking around the edge of lily pad. The insect is sitting in the middle of the pad watching the spider. How would the insect describe its own motion? How would the insect describe the spider's motion? How would a bird sitting on the edge of the stream describe the motion of the insect and the spider? After setting the class to work discussing the questions, the teacher walks around the room listening to the discussions. Ms. M. asks the students to write answers to the questions she posed; she suggests that the students use diagrams as a part of the responses.

The school principal had been observing Ms. M. during this class and asked her to explain why she had not followed her original lesson plan. Ms. M. explained that the girl had made a similar statement to the class twice before. Ms. M. realized that the girl was not being disruptive but was making a legitimate point that the other members of the class were not grasping. So Ms. M. decided that continuing with the discussion of motions and forces would not be fruitful until the class had developed a better concept of frame of reference. Her questions were designed to help the students realize that motion is described in terms of some point of reference. The insect in the middle of lily pad would describe its motion and the motion of the spider in terms of its reference frame, the lily pad. In contrast, the bird watching from the edge of the stream would describe the motion of the lily pad and its passengers in terms of its reference frame, namely the ground on which it was standing. Someone on the ground observing the bird would say that the bird was not in motion, but an observer on the moon would have a different answer.