本文估计扩展t的影响he school day during elementary school on students' education outcomes later in life. We do so in the context of Mexico City's metropolitan area, where a large-scale program introduced in 2007 extended the school day from 4.5 to 8 hours in schools that adopted the program. We exploit cohort-by-cohort variation in students' full-time school enrollment during elementary school to identify the longer-term effects on their performance in a high-school admission exam, subsequent placement, and preferences over high schools. The results indicate that full-time schools have positive and long-lasting effects on students' performance, increasing high-stakes test scores by 4.9 percent of a standard deviation. Exposure to full-time schooling also increases students' probability of choosing highly-selective high schools as their top choices, especially among students from low-SES schools.