Thirty‐three 7th‐grade mixed‐ability students and 22 11th‐grade honors students were interviewed about their conceptions of models and their use in science. Three analyses are presented in order to: (1) portray the character of students' spontaneous answers; (2) examine the criteria students use to decide whether specific items are models or not; and (3) describe how different general levels of understanding models reflect different epistemological viewpoints. Four experts were also interviewed for purposes of comparison. We found that students in both groups have conceptions of models that are basically consistent with a naive realist epistemology. Thus, they are more likely to think of models as physical copies of reality that embody different spatiotemporal perspectives than as constructed representations that may embody different theoretical perspectives. As student ideas become more sophisticated, however, they increasingly include the fact that models are designed for particular purposes, especially to help communication. All of our experts expressed ideas consistent with a constructivist framework, drawing a distinction between abstract and physical models and articulating ways that models are used for the construction and testing of ideas. Our findings suggest that students need more experience using models as intellectual tools, more experience with models that provide contrasting conceptual views of phenomena, and more discussions of the roles of models in the service of scientific inquiry.

We report on two studies that assess to what extent sixth and seventh graders (a) did not differentiate between weight and density as quantities at the time of the preinterview and (b) made conceptual changes after participating in a curriculum on weight and density that uses computer-based conceptual models and simulations. In Study 1, 18 sixth graders received individual clinical interviews to assess their understanding of the density of materials and their ability to use a concept of density to understand flotation, immediately before and after they worked through an eight-lesson curriculum unit on those topics. In Study 2, 12 sixth graders and 10 seventh graders received individual clinical interviews before and after their classes worked through a more extensive 16-lesson curriculum on these topics and on the topic of changes in density with thermal expansion. In both studies, we found that the majority of students failed to differentiate consistently between weight and density at the time of the preinterview (although within this group, we distinguished between those who were beginning to have some insight that two distinct dimensions might be involved and those who were not), whereas the rest were able to make an initial qualitative distinction between these quantities. We found that our curriculum was moderately effective in helping some but not all children differentiate weight from density and -Requests for reprints should be sent to 222 SMITH, SNIR, GROSSLIGHT in helping other children consolidate their understanding of density. Further, the revised curriculum used in Study 2 seemed more effective than the curriculum used in Study 1. However, the curriculum was not equally effective for all groups of children (those children who had some initial insight that the two dimensions were necessary were helped the most). The experience of using the curriculum alerted us to the specific ways our models were helpful and certain complexities inherent in the process of using conceptual models to produce conceptual change. These complexities are discussed, along with ways to further revise the curriculum that might lead to its more widespread effectiveness with children.

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