Identifying and assessing core knowledge has been and continues to be a challenge that vexes the discipline of sociology. With the adoption of a thematic approach to courses in the core curriculum at Butler University, faculty teaching Introductory Sociology were presented with the opportunity and challenge of defining the core knowledge and skills to be taught across course sections with a variety of themes. This study of students (N = 280) enrolled in 12 sections of a thematically-focused Introductory Sociology course presents our attempt to both define and assess a core set of concepts and skills through a pretest-posttest questionnaire to measure student learning gains relative to: (1) a sociological perspective, (2) sociological theory, (3) research methods, and (4) key concepts in sociology. Results show significant learning gains on all four dimensions, with the greatest gains coming in sociological theory. There were no significant differences in pretest scores by gender or by whether students had taken a sociology course in high school. Seniors scored significantly higher on both the pretest and the posttest, but after we controlled for pretest scores seniors did significantly better only on the subset of questions related to sociological theory. Students who took a sociology course in high school scored lower on the methods subscale of the posttest and had lower overall total posttest scores than their counterparts.