I am actually unaware of the statistic/studies you are referring to, but let's assume it is valid. Is it so surprising that kids whose parents value education highly enough to undertake homeschooling, or, pay for private school, perform better? Kids with parents that value education generally make a strong impression on their children, who in turn, grow to value education. I am not trying to make excuses for public schools here. I think more competition will make them leaner and stronger. I am simply pointing out that correlation does not alway imply causation.