Over the past decade, national initiatives have shifted States' attention to the challenge of turning around low-performing schools. The lack of consistent, dramatic improvements in the lowest-performing schools reflects the severity of the school turnaround challenge, but also suggests the need to continuously evaluate and refine turnaround…

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.…