NEPC Review: Apples to Apples: The Definitive Look at School Test Scores in Milwaukee and Wisconsin (Wisconsin Institute for Law and Liberty, March 2017)
The report reviewed here compares Wisconsin student test score performance for the 2015-16 school year across public schools, charter schools and private schools participating in one of the state’s voucher programs. Comparing a single year’s test scores across school sectors that serve different student populations is inherently problematic. The report uses linear regression models to attempt to adjust for these differences and make what the authors claim are “apples to apples” comparisons. Based on these comparisons, the report concludes that charter schools and private schools participating in the voucher programs are more effective than traditional public schools. Unfortunately, the limited nature of available data undermines any such causal conclusions. The inadequate and small number of school-level variables included in the regression models are not able to control for important confounding variables, most notably prior student achievement. Further, the use of aggregate percent proficient metrics masks variation in performance across grade levels and makes the results sensitive to the (arbitrary) location of the proficiency cut scores. The report’s description of methods and results also includes some troubling inconsistencies. Thus, while the report does present important descriptive statistics about test score performance in Wisconsin, it cannot provide answers for those interested in determining which schools or school choice policies in Wisconsin are most effective.