Prior research has documented that classroom-level variables have a significant effect on student outcomes; however, previous findings have typically focused on average student outcomes and have only recently begun to use hierarchical linear modeling techniques. The present study aimed to investigate the effects of classroom-level variables on the…

Background: Cluster-randomized experiments that assign intact groups such as schools or school districts to treatment conditions are increasingly common in educational research. Such experiments are inherently multilevel designs whose sensitivity (statistical power and precision of estimates) depends on the variance decomposition across levels.…