It's funny that you say that barriers come down, Traalaa, because at any of the state secondary comps near me it's obvious when the children come out in the afternoon that the white children are walking with white children, the black children are with black children, the Muslim boys are together and the Muslim girls are together.
I pass three state secondary schools on my school run and it's the same at every one.
At the primary schools it's the parents who don't mix and stand in their separate groups - black parents, Muslim parents, white English parents and white Polish parents at the one nearest to me. The highest achieving state primary schools have predominantly white middle-class children because the catchment area is full of houses worth £1-2 million. Those schools will be full of children who will do the 11+ and be destined for a private secondary school.
I have friends whose children go to state schools and it's pretty obvious that the children of middle-class home-owning families make their friends with similar children. Hardly any of those children will mix with the asylum seekers or estate children outside school.
The other thing about private education is that most of the children I have come across at DD's prep and now her secondary school actually love school and are enthusiastic about it, and most of the state school educated children I've spoken to see it as something to be got through and describe it as "boring".
Every time I asked one little boy what he had done at his primary school the answer was always, "maths and literacy." Another little boy was pleased that he was going to a particular secondary school "because we finish at 3.00." Neither of those boys can get their heads around the fact that my daughter through choice will go in at 8 am for the school choir and stay until 5 or 6 for sport, and go in at weekends for other activities.
I know there are some great state schools where children are enthusiastic and keen to excel but you will definitely find a higher percentage of those children in private education.