A better vision for development - Eyeglasses and academic performance in rural primary schools in China

Rural primary students in grades 4-6 with poor vision across two counties in western China; randomized by matched township pairs (exact participant count not obtained from abstract or working paper summary)

Grade 4-6 rural Chinese primary school students with poor vision, 2004 intervention year

Township-level randomized trial offering free eyeglasses. The headline estimates are the authors' "preferred" specification, which EXCLUDES township pairs in which control-township students were mistakenly given eyeglasses - a post-hoc exclusion driven by implementation failure, which is the main reason this is graded B rather than A. Abstract does not state whether the achievement measure was an independent standardized test; recorded as unknown rather than assumed. The paper's framing is itself an argument this archive endorses: OLS estimates of vision on schooling are biased because studying harder damages vision, so only randomization identifies the effect.

Wearing eyeglasses for one academic year increased test scores of students with poor vision by 0.16 to 0.22 SD, described by the authors as equivalent to 0.3 to 0.5 additional years of schooling, averaged across the two counties. Benefits were larger for under-performing students. Girls were more reluctant to accept glasses; uptake was also shaped by parental awareness, mothers' education and economic factors. About 10% of primary students in developing countries have poor vision and very few wear glasses.

Low for the treatment contrast (township randomization). The paper explicitly identifies the reverse-causal confound that makes observational estimates useless here: more studying causes myopia, so cross-sectional associations between poor vision and achievement are contaminated in an unpredictable direction.