Class Composition Effects in Achievement and Interest and the Role of the Learning Environment Revisited: A Conceptual Replication and Extension of Lavrijsen et al. (2022)

Class composition is a key contextual factor in students’ academic development. Prior research has mainly focused on class mean achievement, yet less is known about other composition characteristics, possible differences for students with varying initial achievement, and mechanisms transmitting composition effects. Thus, we conceptually replicated and extended recent work on classroom composition effects in mathematics classes (Lavrijsen et al., 2022, Journal of Educational Psychology). Using three-wave longitudinal data from 3,470 German secondary school students (54.8% boys, 30.5% with migration backgrounds), we estimated multilevel models that tested effects of class mean achievement and within-class heterogeneity on individual achievement, cross-level interactions with students’ initial achievement, and mediating effects of differentiated instruction and academic orientation. Extending Lavrijsen et al., we additionally investigated motivational composition effects (class mean level and heterogeneity in academic interest) and analyzed both mathematics and German classes. Compared with Lavrijsen et al., effects of mathematics achievement were smaller and less often statistically significant, underscoring the value of conceptual replications for assessing robustness across contexts. Furthermore, students with higher initial achievement in German benefited more from higher class mean levels. Academic orientation mediated the effect of class mean interest on subsequent individual interest in German. Although heterogeneity in achievement or interest did not predict outcomes directly, differentiated instruction was particularly advantageous in more heterogeneous German classes for both achievement and interest. No comparable effects emerged in mathematics. Overall, the findings highlight the nuanced, subject-specific, and context-dependent nature of composition effects and the importance of replications and extensions for building cumulative knowledge.