Our understanding of health and social stratification can be enriched by testing tenets of cumulative inequality theory that emphasize how the accumulation of inequality is dependent on the developmental stage being considered, the duration and stability of poor health, and the family resources available to children. I analyze longitudinal data from the British National Child Development Study (N = 9,252) to ask: (1) if child health is a source of cumulative inequality in academic achievement, (2) whether this relationship depends on the timing and duration of poor health, and (3) whether trajectories are sensitive to levels of family capital. The results suggest that the relationship between health and academic achievement emerges very early in life and persists and that whether we observe shrinking or widening inequality as children age depends on when we measure their health and whether children have access to compensatory resources.