We analyze the behavioral responses of teachers, schools, parents and students to variation in class size induced by a maximum class size rule applying to Swedish upper primary schools. We find that: i) teachers in large classes appear to use less intensive teaching methods than teachers in small classes; ii) especially low-income students find their teachers hard to follow when they explain in front of a large class; iii) high-income parents respond to larger classes by helping their children more with homework; and iv) low-income parents are instead more likely to respond to larger classes by moving to another school district. These findings indicate that the total policy effect of a class size reduction differs from its direct effect and that this difference varies across students. Taken together, the results may help explain why the total policy effect of class size reduction is larger for low-income students than that for high-income students.