Small-class effects on science achievement in secondary education

Small classes may affect students’ science achievement, but research evidence for small-class effects on science achievement in secondary education has been scarce. To fill this literature gap, this study examines small-class effects on 15-year-old students’ science achievement using the Program for International Student Assessment (PISA) 2015 data from 26 countries including 24 European countries plus U.S. and Canada. To reduce confounding factors and estimation bias, propensity score analysis was conducted to control significant differences between students in small versus non-small classes on important observed covariates. Results indicate that the effects of small classes on science achievement were statistically significant and negative in 9 countries (e.g., Germany) whereas in other 17 countries small-class effects were non-significant. Fixed-effects meta-analysis was utilized to combine effect sizes, and findings reveal that the effects of small classes were significant and negative, suggesting that students in non-small classes had higher science achievement, but the overall effect size was small.