It has long been observed that individuals who participate in endurance sports also tend to excel intellectually. More broadly, young athletes, regardless of sport, tend to academically outperform their sedentary peers, and these educational differences persist into adulthood, with implications for earnings and employment. Nevertheless, few studies provide convincing evidence that this association is causal. This study exploits quasi-random variation in the introduction of a youth running program—Rising New York Road Runners (RNYRR)—in New York City public schools to identify the causal effect of aerobic exercise on short- and medium-term educational performance and health.