In this paper, instructional strategies for sustaining model-based inquiry in an undergraduate chemistry class were analyzed through data collected from classroom observations, a student survey, and in-depth problem-solving sessions with the instructor and students. Analysis of teacher–student interactions revealed a cyclical pattern in which students generated, evaluated, and modified (GEM) hypotheses throughout the course. It is hypothesized that sustained involvement in the GEM cycle contributed to students' engagement with scientific inquiry and model construction and revision. As such, GEM represents a promising approach toward achieving process and content goals in the undergraduate chemistry classroom. © 2007 Wiley Periodicals, Inc. Sci Ed, 91:877–905, 2007