This paper examines the impact of recreational marijuana legalization (RML) on human capital accumulation in the United States. Exploiting the staggered adoption of RML across states from 2010 to 2023, we estimate its causal effect on two core educational outcomes, high school graduation and standardized test scores among middle school students. Using large-scale datasets and event-study difference-in-differences estimator we find that RML reduces high school graduation rates by 0.6–0.9 percentage points and lowers middle school test scores by approximately 14% of one standard deviation. These effects are mediated through declines in parental investment in human capital: RML increases adult marijuana use, reduces parental time with children, worsens the home environment, and raises substantiated cases of child maltreatment. The findings highlight an overlooked intergenerational consequence of marijuana liberalization policies and underscore the need to consider human capital externalities in evaluating their welfare impacts.