Initiation of substance use often starts during adolescence, with tobacco and alcohol use frequently preceding the use of marijuana and other illicit drugs. Studies suggest that a positive school climate may prevent substance use while promoting healthy student behaviors. The purpose of this study was to determine the longitudinal associations…

Randomized experiments are often considered the strongest designs to study the impact of educational interventions. Perhaps the most prevalent class of designs used in large scale education experiments is the cluster randomized design in which entire schools are assigned to treatments. In cluster randomized trials (CRTs) that assign schools to…

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.…