On July 14, the U.S. Department of Education released a study that the teachers' unions are holding up as evidence that public schools are better than private schools. The study doesn't actually show this, and is riddled with methodological flaws anyway. If you tell the average American that public schools are better than private schools, she's likely to respond, "What have you been smoking?" In this case, the evidence shows that the average American is right. The study tells us nothing whatsoever about the relative quality of public and private schools. It takes raw test scores from isolated years and...