I'd just add that another far more eloquent poster than me wrote on another "Private v State" thread that opting for Private is, for a lot of parents, not about wanting to hot house their children to get perfect results or to mix in "higher" social circles, but about supporting their child to find the right environment for them to thrive.
And before I am jumped on, no I am not trying to say that parents who cannot afford Private are not trying their best for their child. Being able to afford Private is a huge privilege and in an ideal world all schools would be fully funded seats of excellence and enrichment, but the fact is that, sadly, they are not.
I've copied and pasted the comment from the other thread below, credit to @Thepeopleversuswork
I don't think the standard of teaching is necessarily always better in private schools (though it seems to be good in my DD's school).
I couldn't give a shit about her playing lacrosse or rubbing shoulders with investment bankers' kids or going on expensive school trips. The additional enrichment activities are nice but not a dealbreaker. Even the class sizes are a nice to have but not essential.
The thing that really clinched it for me was that I desperately desperately wanted to avoid my DD being educated alongside children who think it isn't cool to be educated. Some of her cohort in (mixed state) primary were starting to develop attitudes like this: boys hanging around outside school trying vaping, girls competing with each other for the attentions of these useless no marks, unpleasantly sexual SM and notes being sent around, truancy and shoplifting. All of this becoming a major social preoccupation for the year group.
It was all relatively innocent at at the point where I had to make a choice (year 6) but I could tell where it was heading and I was having none of it. If I had had to double mortgage my house to avoid her growing up around that I would happily have done so. It's the worst possible environment for a child who wants to work to be in at that age.
I'm not saying that this doesn't happen in private school. Private schools are not a panacea: there are bad and damaged kids at private school for sure, there is bullying (occasionally pretty bad bullying) and kids drop out and vape in the toilets and all the rest of it. But private schools, by and large, don't allow a cohort of kids who want to disrupt or belittle other kids to stop them learning to become dominant in a class or year group.
I'm really sorry that this is what's happened to comprehensive education in Britain. But it has, certainly where I live. I was extremely lucky to be able to pay to avoid this and not a day goes by when I don't feel ambivalent and guilty about this as I realise most people don't have that option.
I'm quite sure there are lots of kids in comprehensive schools who thrive despite this. But the bottom line for me is that I didn't want my (vulnerable, shy and anxious) daughter to be permanently in fight or flight mode, having to constantly try to be her best self despite an environment which incentivises her not to. I want the environment, as far as possible, to work in her favour and a big urban comprehensive would not have worked in her favour.