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.…

This study sought to address the lack of experimental research examining the influence of contextual factors on African American students' learning. A total of 162 low-income African American and White fourth graders were randomly assigned to ethnically homogeneous, communally structured groups of three to work on a motion acceleration task using…