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.…

Numerous authors have reviewed research to determine which skills are considered fundamental to successful academic and social outcomes for students (Hattie, Briggs, & Purdie, 1996; Masten & Coatworth, 1998; Wang, Haertel, & Walberg, 1994; Zins, Weissberg, Wang, & Walberg, 2004). These skills include: (1) cognitive and…