This paper examines the external validity of health intervention by comparing the impacts of providing free eyeglasses on the educational performance of nearsighted children in two settings: rural public schools in Western China and urban private migrant schools in Eastern China. The intervention significantly improves educational outcomes by 0.14 standard deviations in math in rural public schools but not in private migrant schools. The difference in measured impacts is due in part to lower quality schooling in migrant schools in Eastern China. Our findings show that only when school is providing a quality education, health interventions might increase student learnings.