The target ideas in these units are informed by the model of progression for evidence outlined earlier and, as previously argued, cover the range of learning outcomes accessible to the majority of fourth-grade students. Some students will still struggle to master these ideas in seventh and eighth grades, whereas the understanding of others will have moved far beyond even the most difficult of these ideas.

A final set of examples deals with the concept of causal explanation—provided in Unit 4 on page 172.

In the examples given for the Worlds Apart topic, each second-order concept is addressed once and once only. If two topics are taught at each grade, it follows that each second-order concept will be revisited at least once each year and that planning for systematic progression across grades is possible.

The examples provided here are, of course, only an illustration of the start of the planning process. Detailed planning with reference to content, materials, and activities must flesh out the key generalizations and ideas exemplified above. At the same time, our planning should also take account of the other key findings of How People Learn. The planning grid presented in Box 3A-2 shows how all three key findings might figure in planning to develop students’ understanding of the concept of evidence, using the St. Brendan and Pilgrims’ tasks as examples.