How consistent are class size effects?

Thus far researchers have focused on computing average differences in student achievement between smaller and larger classes. In this study, the author focus on the distribution of the small class effects at the school level and compute the inconsistency of the small class effects across schools. The author use data from Project STAR to estimate small class effects for each school on mathematics and reading scores from kindergarten through third grade. Then, all school estimates were combined to calculate an overall weighted average. The results revealed that a large proportion of the school-specific small class effects are positive, while a smaller proportion of the estimates are negative. Although students benefit considerably from being in small classes in many schools, in other schools being in small classes is either not beneficial or is a disadvantage. Small class effects were inconsistent and varied significantly across schools in all grades indicating a small class by school interaction.