One of the guys who works for me went to private school (primary and secondary). He is the least confident person I know. He is always seeking validation for his opinions, choices and decisions.
Dh and I went to a low standard comps, ended up with PhDs and now have a well paid jobs with people working for us, quite a few of them privately educated.
My confidence came from my parents who believed in me and told me that I was just as good as anybody else. Parents who send their children to private school have to convince themselves that they are getting something mystical for the money they shed out, imo.
DH and I send our 6yo boys to state schools even though we can comfortably afford private because we believe it is us who will make the difference to our boys inner confidence, motivation and aspiration. I never understand why parents think that this is at school their children will gain their inner confidence, hard work ethic and aspiration. There are 24 hours in a day, children spend 6-7 hours a day at school, about 8-10 hours are spent sleeping, evenings are with parents, weekends are with parents, school holidays are with parents.
Our focus is on making sure our boys are happy, partake in the many opportunities they have access to (they currently are learning the piano, French, attend beavers, swim and soon will sing in a choir). At their state school, they do cricket, football, hockey,dance, read everyday, write, can do algebra already, can point to England, USA, Australia, Nigeria etc on the map,go on many school trips.
In terms of class size, they have TAs (just like private schools) and are taught in ability groups that can number 5 or 6 and that is why the class size argument rarely stands up to scrutiny imo.
I personally don't see private education as value for money because the rewards do not often outstrip the rewards of state educated children in my personal experience.