["Review of Development Economics, Volume 30, Issue 2, Page 1032-1047, May 2026. ", "\nABSTRACT\nWe examine why the education of young girls has historically lagged behind that of young boys across different countries. Using data from 105 countries during 1990–2020, we discover some evidence that is consistent with the idea that parents in many traditional societies reduce investments in the primary schooling of their daughters after they observe other young girls in their communities getting married early. We propose a new “instrument” to address potential endogeneity between child marriage and female primary education: the minimum legal age of female marriage in the country. We observe that this relationship between child marriage and female primary education is more likely to hold in more agrarian countries, where there may be fewer employment opportunities and lower returns to schooling for women. We do not find any evidence that these results vary across countries with different state religions or different beliefs about gender roles. Our results suggest that policies that help reduce child marriage can help reduce the gender gap in education between boys and girls; furthermore, providing opportunities to improve labor market outcomes for women can potentially help decrease both child marriage and the gender gap in education.\n"]