All schools are essentially businesses, but some are run better than others. I was lucky enough to go to a grammar school and while I didn't enjoy it, I genuinely think it helped raise the prospects for a lot of students that went to it.
I think there is a serious problem with a huge number of schools in the UK and if a parent can afford to send their child to private school then why shouldn't they? If I had kids, I'd want to give them the best chance in life that I could afford them. I think private schools focus on the success of the individual much more than the average state school.
I went to a lot of schools, so I've seen a range of different schools. I have been to two very good comps, but I think that while they were great at helping less able kids at passing their exams, they weren't as good at providing support for the already-achieving students. In fact, in a lot of schools (the grammar included) there was a tendency to place more focus and invest more time into kids that messed about and disrupted class. Whilst I'm not saying that disruptive kids should be abandoned, my point is that there is often an attitude that focuses on everyone reaching the minimum expected, and then there is little help for those aiming higher.
I remember asking for extra help at GCSE because I was struggling with learning French (having previously studied Spanish) and I was told that extra classes were only available for selected students who either had some sort of learning difficulty or were disruptive. Some disruptive kids do have things like ADHD or whatever, but some of them just don't give a ****. How is it fair that more time is invested in them than someone who actually does the work?
It isn't fair. And I don't see the educational system improving any time soon, so I'm in favour of private schools, although I've never been to one, but almost all the kids I know who have, for the most part have done well at school and gone on to good jobs and good unis. Some private schools can even offer valuable work experience placements and ways into coveted internships.