About 10% of primary school students in developing countries have poor vision, yet in virtually all of these countries very few children wear glasses. There has been almost no research on the impact of poor vision on school performance in developing countries, and simple OLS estimates are likely to be biased because students who study more often are likely to develop poor vision faster. This paper presents results from the first year of a randomized trial in Western China that began in the summer of 2004. The trial involves over 19,000 students in 165 schools in two counties of Gansu province. The schools were randomly divided (at the township level) into 103 schools that received eyeglasses (for students in grades 3-5) and 62 schools that served as controls. The results from the first year indicate that, after one year, provision of eyeglasses increased test scores by 0.15 to 0.30 standard deviations (of the distribution of the test scores). Data collection for the Gansu Survey of Children and Families was supported by grants from The Spencer Foundation Small and Major Grants Programs (wave 1), by NIH Grants 1R01TW005930-01 and 5R01TW005930-02 (wave 2), and by a grant from the World Bank (wave 2).