Obviously the people who have chosen (been able to choose) private education on this thread have chosen schools they are happy with, and that suit their children. So that leaves out the less good private schools!
I spent 15 years running arts projects in schools, either sustained residencies, or repeat visits, which gave me pretty good ongoing understanding of many many different schools.
Often, education in the private sector seems far more 'conformist', and goal (exam) orientated than in the state sector. The students are far more conformist in outlook, and are attuned to the academic vision mapped out by their parents. Of course this contibutes to good results, but brings the wider disadvantage of conformist thinking, living etc.
Private schools can be set up by a head who has been offered a golden handshake to resign from the state sector (following a bad ofsted for e.g)- who buys a big victorian house with the money, employs some recent graduates on short term teaching contracts (my brother worked for a private school that offered contracts just for sept-june so that they never paid staff over the holidays!) and hey presto.
I saw many many brighht, motivated kids do very well even in difficult sink schols where the averages were brought down by less able/motivated kids. I saw bright children given average unimaginative education in the private sector - and some less bright children be supported to do surprisingly well, in both sectors. And clearly we have heard from people who were allowed to fail and suffere in state education. Friends of mine have just removed a (very bright) child from a highly renowned S London independent school because of high pressure academic competetiveness (extending to bullying) and because of bullying due to not being able to keep up with the ski-ing trips and designer clothing.
Ameriscot says: "The two closest independent schools to me are always right at the bottom of the league tables (close to 0% A-C) and that with fees of £20k a year. Yet they are good enough schools, sending most of their pupils onto top universities - far more than the local (heavily-oversubscribed) comprehensive (35% A-C) could ever dream of. " Doesn't that imply that middle-calss kids brought up to have the confidence to aspire and perform well in a university interview are being supported by average (as in Amerisct's e.g) schools to snap up university places, etc, or that it IS social class that counts, rather than academic results, just as we pinko-whingers have always suspected?
I went to a Direct grant School - an independent school which had 50% of the places paid for by the local authority as scholarship places. The fee-paying places were selective. It worked brilliantly within the school, but embarrasingly we were all totally snobby about anyone who went to a non-selective independent school (we assumed they were thick), but not about anyone who went to a state school!
I am in favour of small classes for all, and would certainly not criticise anyone for sending a child to a private school, but to say private education is better per se is not supportable.