Embodied capital theory (ECT) argues that socioeconomic “modernization” leads to high-cost, high-return parental investments in education, in turn incentivizing demographic transitions to low fertility. However, few studies have directly investigated the proposed opportunity costs of schooling in contemporary developing populations undergoing socioeconomic change. We present a study of children’s time use in two communities in Mwanza, Tanzania, representing either end of a local rural-urban gradient. Consistent with ECT, town residence compared with village residence was associated with increased schooling at the expense of time allocation to children’s work. However, these patterns apply primarily to boys, for whom herding work is relatively incompatible with schooling. Girls more readily combine domestic chores with school attendance, a pattern that may account for unexpectedly high female school enrollment in this population. Furthermore, the strongest time allocation trade-offs were not between school and work but between school and leisure time, suggesting overall low opportunity costs to education. Mixed support for ECT may partially explain why fertility decline has stalled in many low-income countries despite education uptake. Finally, we advocate that international development programs consider the well-being implications of reduced leisure time accompanying education uptake, particularly for girls maintaining a “double shift” of school and domestic work.