A new study by Christopher and Sarah Lubienski presented in their book, "The Public School Advantage", shows that public students do better than their private school peers. Using data from the National Assessment on Educational Progress (NAEP), commonly accepted as the gold standard for assessing student achievement, and a longitudinal study of student beginning in Kindergarten, the authors found that when controlling for demographic background, math scores were better for public school students than private school students. The authors chose math because it is the subject that receives less outside support than reading. The Lubienskis argue that any evidence of differences between performance of public and private school students can be explained by demographics. In other words, private schools cater to advantaged families who have the resources to provide more educational opportunity for their children. This, I think, is the most important point to glean from this study.
The point is not that public schools do better at getting students to achieve on a standardized math test, although certainly we can throw some kudos to public schools which are often much maligned by policy makers and the media. The advantage of private schools is not how students score on achievement tests but on the social capital that they provide. Students in private schools tend to benefit from a distinct advantage of mixing with their advantaged peers. It's why parents send their students to schools like Andover and Exeter. These schools open doors to elite colleges which open doors to elite opportunities. These connections are the private school advantage, regardless of scores on standardized tests. Therefore, if we want to equalize the playing field, so to speak, we would really have to look at privatized education that allows the elite to exit the system where they would co-mingle with the less advantaged such as in Finland. But, truth be told, that's a conversation that this country is not ready for today, if it will ever be.