In this study, the authors investigated the degree to which a family investment model would help account for the association between family of origin socioeconomic characteristics and the later educational attainment of 451 young adults (age 26) from 2-parent families. Parents' educational level, occupational prestige, and family income in 1989 each had a statistically significant direct relationship with youths' educational attainment in 2002. Consistent with the theoretical model guiding the study, parents' educational level and family income also demonstrated statistically significant indirect effects on later educational attainment through their associations with growth trajectories for supportive parenting, sibling relations, and adolescent academic engagement. Supportive parenting and sibling relations were linked to later educational attainment through their association with adolescent academic engagement. Academic engagement during adolescence was associated with educational attainment in young adulthood. These basic processes operated similarly regardless of youths' gender, target youths' age relative to a near-age sibling, gender composition of the sibling dyad, or gender of parent.