This article examines the mechanisms linking health to the educational attainment of adolescents. In particular, it investigates the role of cognitive/academic achievement and a variety of psychosocial adjustment factors in explaining this relationship. Using data from the National Longitudinal Survey of Youth 1997 cohort (NLSY97), we estimate models of timely high school completion and of post-secondary enrollment using both standard logit estimation and sibling fixed-effects models. We find that, net of sociodemographic background and stable unobserved family characteristics, adolescents who experience worse health are substantially less likely to complete high school by their 20th birthday and to transition to post-secondary education. Cognitive/academic achievement and psychosocial factors appear to explain a large portion of these health-related educational deficits. However, adolescent health continues to be significantly associated with these key educational transitions. The findings highlight a potentially important role of health selection processes in generating socioeconomic inequalities in early adolescence to young adulthood. (Contains 5 tables and 2 notes.)