Variability in Pretest-Posttest Correlation Coefficients by Student Achievement Level

State assessments are increasingly used as outcome measures for education evaluations, and such evaluations generally use pretest scores as control variables. The correlation between the pretest and outcome (posttest) measures is a factor in determining, among other things, a study's statistical power. This report examines variability in pretest-posttest correlation coefficients for state assessment data on samples of low-performing, average-performing, and proficient students to determine how sample characteristics (such as achievement level) affect pretest-posttest correlation coefficients.