This research investigates how participation in college-based science-training programs increases student intention to pursue a scientific career. Using identity theory, we delineate three levels of social structure and conceptualize science-training programs as proximate social structures. Results from a sample of 892 undergraduate science students are supportive of identity theory and indicate that participation in proximate social structures leads to increased commitment to a science identity, increased salience of a science identity, and increased intention to pursue a scientific career. This study contributes to the literature on identity theory by demonstrating how participation in proximate social structures can lead to subsequent identity processes, thus refining the understanding of how society shapes the self and clarifying how social positioning affects choices for behavior. Additionally, the conceptualization of proximate social structures provides an avenue for applications of identity theory to investigations of other social interventions as well as mechanisms leading to social inequality. (Contains 2 figures, 5 tables, and 11 footnotes.)