The aim of the "Tools of the Mind" prekindergarten curriculum is to enhance children's executive function skills within an instructional context that promotes the basic academic and social skills that prepare them for kindergarten and beyond. To investigate the effectiveness of "Tools" in achieving this aim, the authors are…

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.…