Moreover, both math tests had been altered prior to the Lubienskis’ data collection to more closely align with the way that math is generally taught in government schools as opposed to private schools. By the Lubienskis’ own admission, “the professional development of math teachers changed in the late 1980s to emphasize math reasoning and problem solving and de‐​emphasize math facts and computations.” Government schools were more likely to embrace the new math curriculum than private schools, which “tended to continue to emphasize traditional math content.” Thus, concludes Wolf, this is a study of “how well private and public school students have learned the brand of math taught in the public schools” rather than a true measure of the differences in math skills.

Wolf also faults the Lubienskis for making apples‐​to‐​oranges comparisons of student characteristics that are “measured differently across school sectors” and for methodological flaws in accounting for students who switched from government schools to private schools or vice‐​versa.

Even more distressingly, the Lubienskis ignore the copious evidence from randomized controlled trials, which are the gold standard of social science research. As Jay P. Greene, Wolf’s colleague at the University of Arkansas, writes: