This dissertation examined the relationships among adoptive status, social capital, and academic achievement. Data from the National Longitudinal Study of Adolescent Health (Add Health) had 609 adopted and 11, 940 non-adopted adolescents. I used OLS regression models to help explain why adopted adolescents have significantly lower grade point averages (GPA) than non-adopted adolescents. Potential mediators were family social capital, closeness to family, mother and father, mothers' and fathers' involvement in their children's education, self-esteem, academic expectations, and in-school behavioral difficulties. Only closeness to fathers and in-school behavioral difficulties differed by adoptive status. Compared to non-adopted adolescents, adopted adolescents were closer to their fathers and had more in-school behavioral difficulties. Adopted adolescents also had lower GPA's, even when all other predictors were in the model. However, were it not for greater closeness to their fathers, adopted adolescents' would have had even more in-school behavioral difficulties and consequently, lower academic achievement. The results have implications for social capital theory and theory and research concerning adoptive families.