All native speakers of Arabic read in a language variety that is remarkably distant from the one they use in everyday speech. The study tested the impact of this distance on reading accuracy and fluency by comparing reading of Standard Arabic (StA) words, used in StA only, versus Spoken Arabic (SpA) words, used in SpA too, among Arabic native…

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.…