This article discusses the effect of international migration on the accumulation of human capital among Mexican youths aged 15–18 who are left behind. Evidence indicates the existence of a negative impact of sibling and parental migration on school attendance among young males but not on the measure of cognitive ability. Migration of extended family members has no significant effect. There is no evidence of a robust effect among females. The negative effect of sibling migration suggests that lower migration costs and differences in return to Mexican formal education between the labor markets of the United States and Mexico could largely explain the negative effect of international migration on human capital.