The authors examine conceptual change in preservice teachers through a synthesis and application of mental models theory. They analyzed longitudinal data in the form of lesson plans, interviews, and written rationales from eight, social science preservice teachers. Findings that illustrate how preservice teachers' mental models changed during their coursework are graphically presented. Preservice teachers' mental models developed from general to discipline-specific practices. However, their conceptions of how students learn continued to focus on learner types rather than learning processes, suggesting a need for an ontological shift. The authors discuss implications for mental models theory and future research in teacher education. (Contains 2 tables and 2 figures.)