There's too much to answer on here.
Most middle class parents move to a posh typor of area to avoid their state educated children being educated with children from very poor homes. It's standard practice 0 you move out of central London to segregate your children in leafy suburbs so it's certainly not a private school thing only. Obviously you have the same differences between different state schools too. Not all those state schools are sink schools so most parents are selecting one they think is the best state school in their area and therefore trying to avoid rough stupid children surely. Why else go by league tables - why else are so many state schools parents obssessed by league tables and getting their children in the best schools?
You work better in class with children or a similar academic standard which is why many comps stream the children. I don't think there's anything radical at all in what I'm saying.
Second issue is yes you can be very disruptive and very clever, of course you can. Indeed I think the best private schools can take the disruptive clever boy or even not so clever boy and draw out the one thing he's good at so he thrives whether that's sport every day or chess club or whatever.
horseshoe's points are interesting. Obviously as 96% of children go to state schools many many of those do very well indeed but statistically the private education gives you a huge great leg up in all sorts of ways so it's a fairly easy way for a parent to do the best they can for a child. If you can afford to pay and don't then arguably the parent is being as bad for the child as if they fed it hamburgers all day or never read to it. We all try to do our best and those that can afford it find paying fees is one of the very best gifts you can give a child. Horse made the point about saying I had suggested her "child will be less respected in this world ". I hope we all respect people whatever their colour sex or schooling.
But what is a fact is that however unfair this is if you say you went to XYZ school or got AAA at A level or worked at ABC company or speak with received pronunciation or whatever people do treat you differently. Of course it can work the other way - go into a left wing environment and in that area you might well find your accent is held against you as indeed might your A level grades but on the whole you tend to be advantaged if you tick the usual boxes.
I still can't see the difference between paying fees go educate your girls in a school with other clever girls and moving to a nice place where the state school girls are all "nice girls" except that my route is honest and the other route isn't.
On the dyslexia thing I think it's a bit of a side issue. You can be very clever with dyslexia and not very clever. You can't generalise. It certainly doesn't make most children disruptive although it can cause some to be disaffected with school which then leads to disruption.
These academic schools have 5 - 10 applicants per place in competitive exams marked without sight or name of the child to ensure no bias. It's a very fair system (except for the fact of payment of fees although there are some who don't pay as some on the thread have said). Most of the children who are clever enough to get in don't get in. It's a lottery in a sense so of course if you're IQ is low or you can't write you aren't going to get in at 11+. It's like any competitive environment but they're lovely inclusive caring schools for those who do get in. I think the private sector has always been better able to cope with difference and delight in it than your average state school. Am I not right that there's more thumping people for being different the lower down the socio-economic classes you go because people are less clever and less understanding and accepting of people who are different?
As for disruption in class I would never pay to have that and private schools have fee paying parents and they know the parents want the children to work in an environment where they stand up when the teacher comes into the room, work well, call the male teachers Sir etc. It's a better way to work.
By the way someone talked about weeding out. Very very very few children are weeded out as far as our experience goes. Occasionally a child may be at the wrong school. At other times they just lose their interest in teenage years and might leave but on the whole the cohort they take in at 5 will run through to 18 at some of these schools. Indeed my oldest her two best school friends from age 5 are all now at 23 by some coincidence all still doing the same thing.
Not sure if I've answered all the questions.
Many parents of children with special needs fight to have them educated separately too - it's a difficult subject and depends on the child and their individual issues.