Countries throughout Latin America and the Caribbean are reforming their education systems to add more hours to the school day. This paper examines the evidence on the relationship between instructional time and student learning, reviewing 19 studies that measure the effects of longer school days in the region. It characterizes the differences in the implementation of extended school day programs and provides one detailed case study and cost-effectiveness exercise, from Uruguay. While the evidence suggests some positive impacts across a range of outcome variables, including learning outcomes, adult labor force participation, and crime and teenage pregnancy reduction, there is considerable heterogeneity across studies. Even using the most optimistic impact estimates, a cost-effectiveness exercise suggests that there are likely many more cost-effective reforms to achieve similar learning effects. The paper concludes with a discussion of the implications for policymakers and practitioners considering an extension of the school day.