Revisiting Class-Size Effects: Where They Come From and How Long They Last

Using data from the Tennessee Student/Teacher Achievement Ratio experiment and subsequent follow-up surveys, we estimate unconditional quantile treatment effects of being assigned to a small-size class and a regular-size class with an aide, compared to regular-size one. Results show that mid-achievers profit the most from being assigned to a small class. Students at the bottom or top of the achievement distribution experience almost no gain. The analysis also reveals a positive and significant effect of a regular class with teacher’s aide for students at the bottom of the achievement distribution, an effect stronger for boys and disadvantaged pupils. In line with previous research, we show that being assigned to a small class during K-3 grades has a positive effect test scores in later grades, on the likelihood of on-time high school graduation, and on taking the ACT/SAT exam. However, these positive effects are driven mostly by students who were high achievers during Project STAR, suggesting that the long-term benefits of being in a small class shrink very quickly for lowand mid-achieving students.