be the recognition that it can be as important to ask why something does not change as why it does.

Likewise, students should come to recognize that both the regularities of a pattern over time and its variability are issues for which explanations can be sought. Examining these questions in different contexts (e.g., a model ecosystem such as a terrarium, the local weather, a design for a bridge) broadens students’ understanding that stability and change are related and that a good model for a system must be able to offer explanations for both.

In middle school, as student’s understanding of matter progresses to the atomic scale, so too should their models and their explanations of stability and change. Furthermore, they can begin to appreciate more subtle or conditional situations and the need for feedback to maintain stability. At the high school level, students can model more complex systems and comprehend more subtle issues of stability or of sudden or gradual change over time. Students at this level should also recognize that much of science deals with constructing historical explanations of how things evolved to be the way they are today, which involves modeling rates of change and conditions under which the system is stable or changes gradually, as well as explanations of any sudden change.


Students’ understanding of these crosscutting concepts should be reinforced by repeated use of them in the context of instruction in the disciplinary core ideas presented in Chapters 5-8. In turn, the crosscutting concepts can provide a connective structure that supports students’ understanding of sciences as disciplines and that facilitates students’ comprehension of the phenomena under study in particular disciplines. Thus these crosscutting concepts should not be taught in isolation from the examples provided in the disciplinary context. Moreover, use of a common language for these concepts across disciplines will help students to recognize that the same concept is relevant across different contexts.

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