CLASS SIZE AND CLASS HETEROGENEITY
利用随机分班数据，研究发现班级规模每增加一个标准差，学生平均成绩下降0.1个标准差，且对女性和高收入学生影响较小；班级性别和能力构成的效应呈倒U型；班级规模减少20人可使月工资提高约80欧元。
We study how class size and composition affect the academic and labor market performances of college students, two crucial policy questions given the secular increase in college enrollment. We rely on the random assignment of students to teaching classes. Our results suggest that a one standard deviation increase in the class-size would result in a 0.1 standard deviation deterioration of the average grade. Further, the effect is heterogenous as female and higher income students seem almost immune to the size of the class. Also, the effects on performance of class composition in terms of gender and ability appears to be inverse U-shaped. Finally, a reduction of 20 students (one standard deviation) in one's class size has a positive effect on monthly wages of about 80 Euros (115 USD) or 6% over the average.