How Consistent Are Class Size Effects?

Evidence from Project STAR has suggested that on average small classes increase student achievement. However, thus far researchers have focused on computing mean differences in student achievement between smaller and larger classes. In this paper, the author focuses on the distribution of the small class effects at the school level and computes the inconsistency of the treatment effects across schools. The author uses data from Project STAR and estimated small class effects for each school on mathematics and reading scores from kindergarten through third grade.