The effectiveness of measles vaccine for postexposure prophylaxis at educational centers was investigated. A total of 166 children who shared the classroom with 10 confirmed cases during the infectious period of cases were studied. Of total susceptible exposed children, 72% (54/75) were vaccinated and 25 contracted measles. Vaccine effectiveness in children vaccinated within 72 hours of exposure was 90.5% (95% confidence interval, 34%–99%).