Purpose: Children who do not develop early literacy skills, especially phonological awareness (PA) and alphabet knowledge, prior to kindergarten are at risk for reading difficulties. We investigated a supplemental curriculum with children demonstrating delays in these skills.Method: A cluster randomized design with 104 preschool-age children in 39…

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.…