in modern science for many reasons. Each is well tested, validated, and absolutely central to its discipline. Each integrates many different findings and has exceptionally broad explanatory scope. Each is the source of coherence for many key concepts, principles, and even other theories in the discipline. Each provides insight into the development of the field, 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. In that way, understanding and describing matter at an atomic-molecular level is truly foundational for later learning in any science. Evolutionary theory is also integrative of many disciplines, ranging from genetics to ecology and geology, and foundational to all aspects of modern biology, geology, and psychology.

Significantly, there were important similarities in the approaches taken by the two design teams that resonate with findings from current research and that might prove valuable to other (future) design efforts. First, the learning progressions were organized around big ideas of disciplinary importance—major theoretical frameworks in modern science—rather than very abstract or domain-general core ideas, such as systems, interactions, model, and measurement, that are considered important cross-cutting themes in the science standards documents. This disciplinary approach fits with the increasing recognition of the importance of specific content and context in thinking and learning and the power of theories to define and organize understandings of particular domains, something that domain-general ideas by their nature don’t have the power to do (see Chapters 3, 4, and 5 for discussions of conceptual knowledge and its role in scientific thinking).

Second, both design teams identified a number of high-level (abstract) ideas that go into building these disciplinary core ideas, but which, unlike the scientific theories themselves, were more accessible at the start of schooling. These foundational ideas, although not elaborated or well-tested theories themselves, can nonetheless be a source of coherence, providing a framework for organizing children’s learning of new facts, inquiry, and explanation. Thus, both the atomic-molecular theory and the theory of evolution were seen as emergent core ideas, creative syntheses that required the progressive elaboration and transformation of these foundational ideas as they were increasingly grounded in empirical data, integrated, and intercoordinated with each other. In these ways, both design teams acknowledged that even young children have important domain-specific ideas that serve as a foundation for their learning and that the development of complex scientific ideas involved both continuities and discontinuities in children’s thinking (two themes discussed in Chapters 3 and 4).

For example, although the idea of evolution via natural selection is a complex emergent idea, it builds on and integrates a wide variety of ideas that

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