Sometimes simple interventions are the best. From research by Glewwe, Park and Zhao.
About 10% of primary school students in developing countries have poor vision, yet in virtually all of these countries very few children wear glasses….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 4-6) and 62 schools that served as controls. The results from the first year indicate that, after one year, making eyeglasses available increased average test scores by 0.09 to 0.14 standard deviations (of the distribution of the test scores). For those students who accepted the glasses, average test scores increased by 0.12 to 0.22 standard deviations….
These are rather large effects; similar tests given to children in grades 5 and 6 in Gansu province show that an addition year of schooling leads to an increase of 0.4 to 0.5 standard deviations of the distribution of test scores, which implies that these impacts are equivalent to one fourth to one half of a year of schooling. Thus providing eyeglasses is a relatively low cost and easily implementable intervention that could improve the academic performance of a substantial proportion of primary (and secondary) school students in developing countries.
It’s interesting that many students/parents refused the glasses.