This study examined 21 preservice secondary teachers as they engaged in activities aimed at fostering an understanding of the epistemic roles that models, theory, and argument play in scientific inquiry. Findings indicate that instruction can help preservice teachers develop more sophisticated understandings of scientific models and promote incorporation of model-based lessons in their classrooms. However, even with scaffolding, the majority of these preservice teachers were unable to use theoretical models to ground their own empirical investigations. Two factors shaped participants' thinking about these inquiries. One was previous school-related research experience, which influenced not only what they recognized as models but also the way they believed models could be incorporated into inquiry. The other was a widely held simplistic view of "the scientific method" that constrained the procedures and epistemic frameworks they used for investigations. On the basis of these findings, the authors offer a more focused, evidence-based design for instruction around model-based inquiry. (Contains 3 tables, 2 figures and 3 notes.)