The effects of class size on academic achievement have been studied for decades. Although recent research from randomized experiments points to positive effects of small classes, the evidence about the social distribution of effects is less clear. Some scholars have contended that the effects of small classes are larger for minorities and the disadvantaged. These claims have led to policy decisions to implement small classes to reduce inequality in educational outcomes. This article investigates possible differential effects of small classes on achievement using data from Project STAR, a four-year, large-scale randomized experiment on the effects of class size. The small class effects on both reading and mathematics achievement are somewhat larger for minorities and low socioeconomic status (SES) students. However, the differential effects for minority students (interactions) are statistically significant only for reading achievement in one of the models examined, but not others. None of the differential effects of small classes for low SES students are statistically significant. Thus, while there are unambiguous positive effects of small classes on both reading and mathematics achievement, there is no evidence of differential effects for low SES students and only weak evidence of differential effects for minority students in reading achievement.
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