The art of developing and utilizing curriculum materials to foster understanding involves, as Bruner puts it, an active conversation between learners and materials:

For decades, scientists and science educators have struggled to develop curriculum materials that support frequently changing definitions of scientific literacy. Today, definitions of scientific literacy include understanding specific concepts in science, and also being able to engage in several kinds of complex reasoning including distinguishing salient from irrelevant information, explaining and predicting scientific events, reading with understanding, and evaluating and applying evidence and arguments appropriately (National Research Council, 1996).

Curricular reforms in science often represent one-shot interventions intended to develop an understanding of scientific facts or complex reasoning skills in as little as a few days or weeks, despite the suggestion from theories of learning (e.g., Bransford, Brown, & Cocking, 2000) that the development of conceptual knowledge in science takes years and multiple exposures. Although many science programs outside the United States support sequential building of concepts and reasoning (e.g. Japan; see Linn, Lewis, Tsuchida, & Songer, 2000), American precollege science curricula rarely take into account the organized, longitudinal development of science concepts or reasoning skills.