I'm sorry Boazer, but I've got to take issue with some of your list:
'Parents who pay for education are by definition interested in their child's education and therefore are likely to be supportive at home too .(not to say other parents aren't but a much larger proportion are likely to be in the private sector)'
Are you seriously saying that people who don't send their children to private school because (whisper it) they might not earn enough money or prioritise their spending in different ways aren't interested in their children's education? I really take issue with that. It is the most ridiculous, patronising and frankly snobby generalisation I've heard. If you want generalisations, I could also say that parents who pay for boarding education aren't in the least bit interested in having their children around and want rid of them. Bloody ridiculous.
'Private school pupils come mainly if not exclusively from a class which expects to achieve academically and attain good jobs as a result.'
Ditto my point above. Not all private school pupils are upper class, and not all the upper classes expect their children to achieve academically. To generalise again, ime the Asian community also expect their children to achieve academically and attain good jobs, and generally (again) most of them would be described as working class or - shock horror - poor.
Sorry if this sounds stroppy, but those comments have really wound me up, both as a teacher in the state sector and as a state-educated person who has a degree from York University, an MA and whose parents always had high expectations of her.