Little is known about the mechanisms by which extracurricular participation in high school influences educational attainment in young adulthood. Also limited is an understanding of the different types of extracurricular participation and how various activities may manifest within the relationship. The purpose of this study was to examine the link between high school extracurricular participation and educational attainment, with social capital, parental expectations, and academic achievement presented as mediators. Additionally, the present study will explore socioeconomic differences in the proposed relationships. The sample consisted of 5,239 ninth through twelfth graders from the National Longitudinal Study of Adolescent Health (Add Health). Structural equation modeling (SEM) and multiple-group SEM were used to test pathways. Extracurricular participation was categorized into sports participation, non-sport participation, mixed participation (including both sport and non-sport), and no participation. Social capital, a latent factor, was measured by the latent variables of family and school capital. Various indicators of family closeness and inclusion of school culture from survey items operationalize social capital. Parental expectations, another latent factor, was measured by one survey indicator using the question of how disappointed would your resident father and mother be if you did not graduate from college. Academic achievement was measured by grade …