nation is most relevant to the task at hand. A younger child may think hammers are used for hammering nails and not at first realize that they can also be used for sealing a paint can lid. When she realizes the relevance, she can use the tool immediately. The same pattern can happen with conceptual systems as tools. Shifting relevances in themselves may or may not be related to conceptual change. We have already seen how a child may undergo conceptual change in an area but still fall back on an older system because she doesn’t fully realize the relevance or value of the new one. When the relevance is made clear, the child may suddenly use the system with ease.

One example occurs in the development of biological thought: younger children may interpret a property, such as “sleeps,” in psychological terms and thereby judge that simple animals do not sleep (Carey, 1985). Yet when the same children are primed with a very brief context indicating that sleeping can also refer to how the body works, they will instantly attribute sleeping to a much broader array of cases (Gutheil, Vera, and Keil, 1998). The most relevant domain of explanation for a particular task may often come from experience with alternative framings or even from general cultural practices (Atran, Medin, and Ross, 2004).

It is therefore essential, when encountering developmental changes in children’s ability to reason about various problems in the sciences, not only to understand the kind of conceptual change that is involved, but also to understand that some dramatic changes in performance ability may be largely unrelated to any underlying changes in conceptual understanding. As an adult, one can easily see how this is the case by considering how one’s ability to understand a complex scientific phenomena may evaporate in the face of powerful cognitive distractions, massive sleep deprivation, or other factors that reduce the efficiency of cognitive processing. A sleep-deprived person hasn’t really undergone regressive conceptual change; he simply has lost access and may not be tracking as well cues to the relevance of the best conceptual system. As mentioned earlier, however, memory and attentional changes can sometimes also be linked to conceptual change and, in such cases, bring conceptual change back into the process of developmental change.

CONCLUSIONS

As children enter elementary school, the pace of change in their knowledge and understanding of the natural world continues and sometimes seems to dramatically accelerate. Thus, while they bring much with them to the classroom from their preschool years, they launch into quite extraordinary expansions of their knowledge and understanding between kindergarten and grade 8. Understanding how their knowledge growth unfolds and can be supported requires an appreciation of the connections with earlier forms



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