Effects of Class Size on Academic Achievement and Emotional and Behavioral Problems:

Abstract

The present study examined effects of class size in elementary and middle school on students' academic achievement and emotional and behavioral problems, while addressing some important methodological issues. Adoption of a natural experimental design in which class size was determined only by enrollment by grade prevented confounding bias and reverse causation due to the schools' discretion. The hierarchical nature of the data was modeled using a cross-classified model, a kind of multilevel model. The elimination of between-school variation by school-mean centering enabled a test of the pure within-school effects of class size, and avoided confounding by school enrollment. Data were collected from 4th-to 9th-graders in a 9-wave longitudinal investigation (N=45,694). Analysis of these data revealed that an increase in class size resulted in (a)a reduction in students' academic achievement, (b)a decrease in support from teachers, (c)a decrease in support from peers and in prosocial behavior, and (d) an elevation in the students' depression. These results suggest that class size may be a critical variable in class management, due to its extensive influence on the functioning and psychosocial adjustment of students.