Like many in their field, Christopher and Sarah Lubienski, education professors at the University of Illinois, had long taken it as a given that private schools generally outperform public schools. Why would parents shell out thousands of dollars a year in tuition if they weren’t getting more for their money? Moreover, studies in the 1980s and ’90s had apparently settled the matter, showing that private schools produced higher test scores even when accounting for the demographic differences between public and private.
But more recently, when she was working on a study of math instruction, Sarah Lubienski came across a result she didn’t expect. When she divided the schools she was looking at into public and private categories and controlled for demographics, the schools stacked up quite differently. Public schools seemed to be producing better test scores than private. They were also doing better than charter schools.