The Effects of Class Size on Student Achievement: New Evidence from Population Variation
利用649所小学各年级人口纵向变异，识别班级规模对学生成绩的影响，发现无统计显著效应，排除中等效应（班级规模减少10%仅提升成绩2-4%标准差）。
I identify the effects of class size on student achievement using longitudinal variation in the population associated with each grade in 649 elementary schools. I use variation in class size driven by idiosyncratic variation in the population. I also use discrete jumps in class size that occur when a small change in enrollment triggers a maximum or minimum class size rule. The estimates indicate that class size does not have a statistically significant effect on student achievement. I rule out even modest effects (2 to 4 percent of a standard deviation in scores for a 10 percent reduction in class size).