This article presents a problem-based learning (PBL) model for teaching a college U.S. history survey course (U.S. history since 1890) designed to promote postformal thinking skills and identify and explain thinking systems inherent in adult complex problem-solving. We also present the results of a study in which the outcomes of the PBL model were compared to the outcomes of the same course taught with traditional lecture and discussion. The PBL model was more effective in scaffolding learning so that students recognize and practice postformal thinking dynamics and in facilitating self-reported student perceptions of increased course engagement and content relevance. We offer recommendations for implementing PBL in social science survey courses.