This paper presents results from a randomized trial in Western China that offered free eyeglasses to 1,528 rural primary school students. The results indicate that wearing eyeglasses for one year increased average test scores of students with poor vision, and that the benefits are greater for under-performing students. A simple cost-benefit analysis suggests very high economic returns to wearing eyeglasses, raising the question of why such investments are not made by most families. Girls are more likely to refuse free eyeglasses, and that lack of parental awareness of vision problems, mothers’ education, and economic factors (expenditures per capita and price) significantly affect whether children wear eyeglasses in the absence of the intervention.