This study investigated the long-term effects of social disadvantage on academic achievement and on subsequent attainments in adulthood. The study drew on data collected for over 30,000 individuals born 12 years apart, following their development from birth to adulthood. The pathways that link social disadvantage to individual development across the life course were analyzed in a developmental-contextual systems model. The results showed that the influence of risk factors associated with socioeconomic disadvantage depended on the developmental stage of the individual, the experience of long-term or continuous disadvantage, and the overall sociohistorical context. Early risk had a moderate influence on the formation of individual competences. The greatest risk was associated with persisting and accumulating experiences of socioeconomic disadvantage throughout childhood and adolescence. Material conditions improved for the later-born cohort, yet pervasive social inequalities existed that affected outcomes during childhood and were consequently reflected in adult attainment.