1. Generating and evaluating scientific evidence and explanations. The arguments from evidence that support atomic-molecular theory depend on children’s abilities to measure such properties of matter as mass and volume consistently and accurately, as well as their commitment to ideas about the nature of these properties (for example, that mass/weight is a reliable indicator of the amount of matter). Furthermore, they must use these measurements in the context of arguments that require a commitment to logical consistency in predictions and explanations and that involve the coordinated use of model-based reasoning, analogies, and thought experiments.

  2. Understanding how personal and scientific knowledge are constructed. In developing an understanding of the atomic-molecular theory of matter, students need to appreciate that the epistemological standards that are central to science and that are used in deciding between competing views (e.g., explanatory scope, rigor, and precision, ability to integrate large patterns of data, generativity of new testable predictions) are actually different from those typically used in everyday life (e.g., consistency with immediate perceptual experience or initial intuitive ideas—standards less dependent on long chains of reasoning and that have a closer match with surface reality or appearance). Thus, mature scientific theories will often embrace core tenets that on the surface seem implausible or even unintelligible to the novice as long as these assumptions are needed to explain a large pattern of data, are supported by a logical chain of reasoning, and can provide detailed explanations of why surface appearances are misleading. The atomic-molecular theory is a clear case in point. The reason scientists believe in the existence of discrete tiny particles in different arrangements and constant motion (i.e., atoms and molecules) is not because of simple, direct perceptual evidence for such a theoretical analysis; rather it is because of the theory’s tremendous explanatory power and scope and detailed experimental support.

Thus the strands of scientific proficiency can be used in conjunction with the research to develop understandings in middle school students that build on their learning in elementary school and that lay the foundations for reasoning about matter using atomic-molecular models in many different contexts in the life, earth, and physical sciences. With appropriate preparation and teaching, students can engage in true model-based scientific reasoning. They can come to appreciate both the power of scientific models to predict and explain a diversity of phenomena, and how those models are grounded in careful collection and evaluation of scientific evidence.

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