Do They Teach Statistics In Public Schools?

Apparently not, given the laughably-flawed study which claims public schools do a better job than private schools in educating students:

In fact, it makes perfect sense that within each racial and socioeconomic group it’s the low performers whose parents will be motivated to make the sacrifices necessary to put them in private schools. What counts is whether those students make better or worse gains over time after they enter private school — and that’s just what this study can’t tell us.

I could go on, but instead I’ll let the authors explain it for themselves. Buried in the back of the study, they write:

NAEP data [the test score set they use] do not allow for examinations of growth in achievement over time, nor do they include information about student movement between school sectors. Therefore, correlations between school sector and achievement are not demonstrably causal. In other words, one cannot conclude from this analysis that public schools are more effective at promoting student growth than private schools.

Read that last sentence again: One cannot conclude from this analysis that public schools are more effective at promoting student growth than private schools.

So what about all the huffing and puffing in the front of the study — “At this time when market-style reforms are changing the public school landscape, this study offers fresh evidence that challenges common assumptions about the general superiority of private schools,” etc.? It’s just smoke and mirrors.

As it happens, there’s a large body of very high-quality research that does allow us to evaluate the causal connection between school type and student achievement, and it overwhelmingly finds that private schools do better. The most convincing evidence comes from seven studies using “random assignment,” the same method used in medical trials. In all seven studies, students who won a random lottery to use a school voucher at a private school had significantly greater test-score gains than similar students who lost the lottery and stayed in public schools. Numerous studies using other methods have also produced a very strong consensus in favor of this finding.

As a general rule, whenever a researcher announces that his study finds something that contradicts all the other empirical evidence, and the finding just happens to coincide with the self-interest of powerful political groups, it’s a good idea to do a reality check. One can only hope this study doesn’t damage the chances that more students will be empowered to attend superior private schools through voucher programs.

You don't need to be a statistician to figure this one out.

If public schools are better, then why are people willing to pay through the nose for private school tuition when they get public school education for "free"?