Many science education researchers have argued that learners' commitment to a substance (matter-based) ontology impedes the learning of scientific concepts that scientists typically conceptualize as processes or interactions, such as force, electric current, and heat. By this account, students' tendency to classify these entities as substances or properties of substances leads to robust misconceptions, and instruction should steer novices away from substance-based reasoning. We argue that substance-based reasoning can contribute to the learning and understanding of these very same physics concepts. Our case study focuses on a group of elementary school science teachers in our professional development program. Starting from substance-based metaphors for gravity, the teachers build a sophisticated explanation for why objects of different masses fall with the same acceleration. We argue that, for conceptual, epistemological, and affective reasons, instructional interventions should focus on tapping these productive substance-based resources when they arise rather than attempting to suppress them.

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Students in inquiry science classrooms face an essential tension between sharing new ideas and critically evaluating those ideas. Both sides of this tension pose affective risks that can discourage further discussion, such as the embarrassment of having an idea rejected. This paper presents a close discourse analysis of three groups of undergraduate physics students in their first discussions of the semester, detailing how they navigate these tensions to create a safe space to make sense of physics together. A central finding is that students and instructors alike rely on a common discursive resource -epistemic distancing -to protect affect while beginning to engage with ideas in productive ways. The groups differ in how soon, how often, and how deeply they engage in figuring out mechanisms together, and these differences can be explained, in part, by differences in how they epistemically distance themselves from their claims. Implications for research include the importance of considering the coupled dynamics of epistemology and affect in collaborative sensemaking discussions. Implications for instruction include novel ways of encouraging classroom discussion.

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