Science, as with all cognitive activities, is fundamentally a matter of interpretation, sense‐making, and explanation. This study focused on a small group of middle school students as they developed understanding of a particular type of phenomena: emergent systems. Such systems are notable in that macro‐level properties emerge as the result of micro‐level interactions between system components. I describe students' initial understanding of emergent systems, as well as the ways in which their thinking came to reflect the following heuristics: (a) recognition that there may not be a singular causal force underlying the system; (b) distinguishing between micro‐ and macro‐levels of analysis; and (c) comprehending that even small changes at the micro‐level can have significant effects at the macro‐level (Resnick, 1994). I conclude by considering some implications for science education. © 2000 John Wiley & Sons, Inc. J Res Sci Teach 37: 784–806, 2000

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Previous work suggests that children largely perceive science as the passive observation and recording of events. In contrast, studies of practicing scientists show a concern with building and testing models. In this study we investigated the role of a design context for developing children's understanding of science as the construction and revision of models. Grade 1-2 children were given the task of building a model that works like a human elbow. Via discussion, model building, evaluation, and revision, children came to understand that not only motion but also constraints on motion were important qualities to include in their models. Moreover, review of classroom activity and analysis of the postmodeling interview suggest that as early as first grade, children's model-evaluation skills may be quite amenable to development: In comparison to a nonmodeling peer group, modelers were largely able to ignore perceptual qualities when asked to judge the functional qualities of models. Further, they showed an understanding of the modeling process in general that was similar to that of children 3-4 years older.

Recent work on scientific reasoning has largely focused on either domain-specific content knowledge or domain-general reasoning knowledge. This study investigated the interaction between the 2 types of knowledge in a real-world domain in which strict control of variables was not possible. We used a context, sinking objects, in which 10-, 12-, and, 14-year-old children's strong a priori beliefs could be revealed by participant-designed experiments. The results showed that most children initially believed weight alone determined an object's sinking rate. Older, but not younger, participants typically viewed experimentation as a means of exploring the effects of attributes other than weight. However, experimentation did help all children to understand the effects of object shape and material on sinking rates. The results suggests a number of questions for further research, including how children come to understand experimentation as a matter of evaluation rather than demonstration, and the role of unexpected experimental results in driving conceptual understanding.

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