I went to a highly respected academic selective independent school, my siblings went state. One grammar, one comprehensive.
We all have exactly the same level of higher education and roughly ‘equal’ jobs.
I think the education my Dc are getting in comprehensives is as good as mine was. My misgivings are about the NC , not the teaching.
What I did see at my private school (and we recognised it at the time) was that it propped up the ‘second tier’ and more average ability girls to do well, and gave the ones who were not self starters s bit of a helping hand and boost.
My 2 eldest are cleverer than I was and zooming through top grades in top sets at comps, alongside very high achieving peers.
I wish my parents had saved their money for their pensions.
I am always surprised that people think it is ‘not worth it’ for middle ability kids. IMO they might be the ones to benefit most, with more of the propping up.
And there are lots of local and specific factors of course.
But shock horror: the comps my kids go to have police at the gate at going home time. It isn’t always the badge of doom that MN posters seem to think it is. Both schools are S London comps with outstanding status.