This is a pointless question. I've had experience of both and you find thick state school kids, but also thick private school kids. But you also find very clever state school kids and very clever private school kids (which is what a lot of jealous state schoolers tend to forget as many seem to believe that we are all privileged, snobbish toffs who are destined to become billionaires). The aforementioned snobs don't really exist at the vast majority of private schools (which are definitely not all Etons and Harrows as many people seem to think; most are a lot more modest in their means). So I guess this question doesn't really have an answer, since obviously you can't equate a parent's money with their child's intelligence, and although at some selective private schools and state grammar schools there will be a few more clever kids than is the norm, you find a healthy mix of abilities at both private and state schools. And P.S, a private school education isn't a million times better than a state school one like so many seem to think; private schools still have some awful teachers and almost everyone has access to specifications, textbooks, past papers and a trillion resources online nowadays regardless of which school system you are in. Its up to you to make the best use of them.