This paper investigates the effects of California's billion-dollar class-size-reduction program on student achievement. It uses year-to-year differences in class size generated by variation in enrollment and the state's class-size-reduction program to identify both the direct effects of smaller classes and related changes in teacher quality.…

Intuitively, class size reduction is a good idea. Parents support it because it means that their children will receive more individual attention from teachers. Teachers like it for the same reason and also because it creates a more manageable workload. It is generally assumed that the fewer students in a class, the better they will learn and the…