Argumentation and repeated application of new ideas are both important and may involve complementary, but also mutually supportive, processes. Argumentation is a more explicit “meta-process,” whereas repeated practice in application involves (in part) gaining lower level associative strength. At the same time, argumentation from patterns of evidence involves practice in application, and repeated application can also provide additional opportunities for metacognitive reflection. Indeed, many science educators believe that a key to promoting conceptual change in the classroom is to create a more reflective classroom discourse that is structured around explicit argumentation (Hennessey, 2003; Herrenkohl and Guerra, 1998; van Zee and Minstrell, 1997). In addition, longitudinal studies of conceptual change highlight the importance of elaboration and depth of coverage (Clark and Linn, 2003), opportunities to revisit key ideas introduced in benchmark lessons (diSessa and Minstrell, 1998; Minstrell, 1984; Minstrell and Kraus, 2005; Roth, Peasley, and Hazelwood, 1992), and continued use of key ideas in subsequent courses in which they are further elaborated (Arzi, 1988).

Developmental Change That Is Not Conceptual Change

It is important to note that not all developmental change in performance on science-related tasks involves conceptual change. Some kinds of change can often appear superficially to be conceptual change but in fact may be quite different. Consider cases of increasing access to conceptual systems and increasing relevance. Increasing access can be illustrated by an analogy of a child learning to use a heavy hammer. The child may only be capable of using the hammer to hit nails at eye height or lower, as the hammer is too heavy to use for higher level objects. As her arm gets stronger, she can use the hammer in new tasks. Her basic skills at hammering may not have changed in important ways, only her general arm strength. Similarly, a child may have a conceptual system that she uses to understand a phenomenon, but because of more general memory or attentional limits, she may not be able to use it in as wide a range of tasks as an older child. Change here may not involve new conceptual insight, but merely increasing processing capacity, memory storage, or attentional ability. A child who fails to engage in transitive reasoning with a set of inequalities may be failing not because he doesn’t have the concept of transitive relations, but rather because he cannot remember as many relations as an older child. When that memory is assisted, he can see the transitive relations as well (Bryant and Trabasso, 1971). Thus, some tasks may, for cognitive reasons not related to conceptual change, prevent a child from accessing the needed conceptual systems.

In other cases, a child may be able to access a conceptual system but may have a different default bias for thinking about which system of expla-

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