phenomena (Lee et al., 1993; Snir, Smith, and Raz, 2003). In addition, they often are presented with such an impoverished view of the atomic-molecular theory (e.g., no discussion of atoms and molecules as discrete particles separated by empty space or of the role of bonds in holding particles together) that students cannot possibly understand how to explain macroscopic phenomena in atomic-molecular terms (Nussbaum, 1998).

Fortunately, innovative approaches to teaching students about atoms and molecules indicate that middle school students can engage with these issues and benefit greatly from teaching approaches that encourage them to think through these issues (Lee et al., 1993; Meheut and Chomat, 1990; Nussbaum, 1998; Snir, Smith, and Raz, 2003; see Chapter 8 for a discussion of some of these innovative teaching approaches.) Further, there is evidence that being able to think about matter in atomic-molecular terms feeds back and helps clarify children’s understanding of the material nature of gases, phase change, chemical substance and chemical reactions (Lee et al, 1993; Johnson, 1998, 2002).

In short, it takes many years to work out the subtleties of the appropriate constituents of matter and how they combine to create larger units all the way up to those that are macroscopically observable. As children try to figure out these relations, they do make a large number of mistaken inferences about the nature of matter and its transformation. Above and beyond those mistakes, however, are some more accurate beliefs about the different kinds of matter, some sense of conservation, and what sorts of properties are likely to be the most useful in identifying substances.

An Expanding Theory of Psychology

We have explained that infants and preschoolers are acutely sensitive to intentional agents and that they make a wide range of causal attributions about intentional agents that they do not make for other kinds of agents. By the end of the preschool period, they have learned how to think about the relations between true and false beliefs and actions in contexts related to those beliefs. These insights, however, are only the beginning of a long process of increasingly subtle insights into the workings of the minds of others, insights that continue well into adolescence. For example, only in the middle of elementary school do children start to clearly understand that an individual can simultaneously have two conflicting desires or beliefs (Choe, Keil, and Bloom, 2005). Similarly, it can take many years to understand that different people might see ambiguous events quite differently because of the different expectations or biases they bring to the situation (Barquero, Robinson, and Thomas, 2003; Mills and Keil, 2005; Pillow and Henrichon, 1996). The more subtle consequences of thought, such as that cognitive inferences can be sources of knowledge, also take time to develop (Pillow



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