Class Composition, Student Achievement, and the Role of the Learning Environment

Educational Impact and Implications Statement In a sample of 2,895 Grade 8 students from 158 classes, students were found to achieve better when they were in a class with a high mean achievement level, after accounting for previous achievement, intelligence, gender, and social background. By contrast, class heterogeneity (i.e., the extent of between-student differences) was largely unrelated to subsequent student achievement. Hence, while sorting students according to ability could benefit those sorted into high ability classes (given the benefits associated with being in a class with a high mean level), this would come at the expense of those sorted into low ability classes. Moreover, teachers in heterogeneous classes appeared to differentiate their instruction more to student capacities, which was subsequently related to higher student achievement. This study considers how class composition, in terms of between-student variability and the average level of achievement, is related to the academic development of students, and how these relationships can be explained by features of the class learning environment. At the start of secondary education, Flemish schools can decide autonomously how to group their students, leading to variation in class mean and class heterogeneity between classes. In a sample of 2,895 Flemish students from 158 classes, math achievement at the end of grade 8 was found to be unrelated to class heterogeneity, after accounting for previous achievement, intelligence, gender, and social background. Path analyses showed that class heterogeneity was positively associated with teachers' use of differentiated instruction to accommodate for differences between students, and that differentiated instruction was related to higher student achievement. Second, students were found to achieve better in classes with high average achievement. While this held true for all students, high achieving students seemed to benefit the most from being in a class with a high average level. Although class-average achievement was positively related to the academic orientation of the class, this did not explain the association between class mean level and achievement. These results suggest that, although it might be beneficial for the students in the high ability groups, grouping students in distinct classes according to ability might have little overall benefit, and emphasize that teachers' responses to student diversity might be more decisive for improving student achievement than homogenizing classes in terms of ability.