The enthusiasm for science displayed by students in early elementary grades is unparalleled. If not nurtured in elementary school, the spark for learning science diminishes. Unfortunately, the amount of time spent on science in Grades 1-4 has steadily declined since the passage of the No Child Left Behind Act of 2001. In 2012, the National…

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.…