In this paper, we investigate the context-dependence of genetic influences on human capital formation in Denmark. We show that the returns to genetic endowments are smaller for individuals who have experienced childhood disadvantage. We discuss how we can rule out omitted variables or measurement error bias as explanations, because we observe the attenuation effect of childhood disadvantage in both between-family and within-family analyses. Our results highlight an important mechanism driving the persistence of disadvantage across generations. We show that children who experience childhood disadvantage are not able to fully realize their educational potential, even in the context of the generous Danish welfare state.