Using the life course cumulative advantage/disadvantage (CAD) perspective, this study examines the influence of early family SES on trajectories of depressive symptoms spanning from early adolescence to early adulthood, as well as variations in SES-based inequality in depressive symptoms trajectories over this period. This study looks at direct influences of family SES and SES-age interactions (exposure-dependent CAD mechanisms), as well as indirect influences through SES-linked youth experiences (path-dependent CAD mechanisms) to explain variations in SES-based inequality. Data was derived from the Add Health study- a national longitudinal survey of 14,000 adolescents. Results showed large and significant effects of early family SES and associated factors on depressive symptoms in early adolescence, but diminishing effects in middle and late adolescence, supporting the hypothesis of equalization in adolescent health across levels of SES. Disparities in depression reemerged as adolescents entered adulthood, supporting the view that SES-based health equalization is only a temporary process. These findings also strengthen the concept of life course CAD processes, stemming from family characteristics, coming into play later in life. Early family SES was directly and indirectly related to a set of transition-related risks and challenges during emerging adulthood, to which young adults from families of higher SES responded more effectively than those of lower SES. This paper discusses theoretical and methodological implications of the findings.