  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
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, when it
supports learners' sense-making, can form the seeds for sophisticated
understanding of these very same physics concepts. We present a case study of a
group of elementary school science teachers in our professional development
program. The teachers build a sophisticated explanation for why objects of
different masses have the same acceleration due to gravity, starting from
substance-based metaphors for gravity. We argue that, for conceptual,
epistemological, and affective reasons, instructional interventions should
focus on tapping these productive matter-based resources rather than attempting
to replace them.
