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.…

Three decades of mounting academic and testing requirements are snagging growing numbers of students in the 9th grade. "The bulge" is the name education researchers give to the percentage increase in students in the 9th grade over the same period. This article reports on factors that might explain the growing 9th grade bottleneck and…