This study examined the relationships among identified regulation, physical self-concept, global self-concept, and leisure-time physical activity with a sample of middle and high school girls (N = 319) enrolled in physical education. Based on Marsh's theory of self-concept, it was hypothesized that a) physical self-concept would mediate the relationship between identified regulation and global self-concept and b) physical self-concept would mediate the relationship between identified regulation and leisure-time physical activity. Data analysis revealed a structural model in which physical self-concept mediated the relationship between identified regulation and global self-concept as well as the relationship between identified regulation and leisure-time physical activity. Findings provide support for examining self-concept from a hierarchical and domain-specific perspective. Results also offer greater understanding about one possible mechanism that links physical education to increases in global self-concept and leisure-time physical activity, which are considered important outcomes of quality education.