I went to a comp in the late 70s/early 80s where we still did CSEs and 'O' levels, and had setting and streaming, which seemed to work. I did all my secondary schooling up to my 'O' levels there. I went to sixth form elsewhere, as my comp didn't have a sixth form.
I taught for 5 years until recently. I did 2 terms in a private school, and the rest in comprehensives. For me, the private side won hands down. It had small class sizes; an expectation about standards of behaviour; set sanctions if these standards were not adhered to; it set the students, which then meant that differentiation was easier and more targetted. It is far simpler to differentiate for a setted class of 12-15 than it is for a class of 32 mixed ability students. The private school had large playing fields; sport every afternoon; a decent standard of school meals; it also recognised that one size does not fit all.
I feel that we are entitled as tax payers to expect that the money invested in the education system should be distributed fairly, which it isn't at present. We are all taxed at set rates; the school funding should be the same per child, except if they are SN where obviously they should receive more, at both ends of the SN spectrum, and that should include the GAT students. Kids in Devon get more than in Cornwall for example. That is down to government choices, not something we can do anything about, other than voting them out. Once this basic inequality is addressed, then perhaps more money can be wisely invested into education to provide smaller class sizes by recruiting more teachers and building more classrooms.
The other thing that needs to change at secondary level is that teachers are no longer judged on their residuals - the number of students that they get through their GCSEs with a better than predicted grade. To be judged solely on this is soul destroying, as it ignores all the work put in lower down the school, and also ignores those students who don't turn up to their exam, or leave it early, or write sod all on their paper. The system doesn't recognise this.
What amazed me one day was reading that government minister had commented that if all middle class fee paying parents put their kids into the state system then it would improve, as the parents would push for the improvement. There is a tacit acknowledgement there that there is a problem with the state system, but I disagree that it is down to the parents to change things - that is what the government is paid to do. If all the students at private schools went into the state system it would crumble as it could not cope with it.
Until I see that the government is putting sufficient investment into the state system and ensuring the breadth of curriculum that the private schools provide, and the facilities, then I would go for the private school option every time, as it demonstrably works. If it didn't, then those who use that option wouldn't pay for it.
The government also needs to stop messing around with educational methods and imposing such rapid changes for teachers to cope with. There is also a problem within some schools on the issue of setting as some teachers are diametrically opposed to it for their own political reasons, which makes my blood boil. Give me a class of lower ability children, and I can work with them, and get their results up. Give me a mixed ability class, and I can't achieve the same effect, as there are simply too many differing levels of ability to cater for and the lesson inevitably goes at a slower pace than one would like.
When I talk to my Danish, Swedish and Finnish friends, there is always disbelief about the state versus private debate in the UK, as their systems of education are such that the state provision is excellent and the need is not there for the way we have set up schooling in the UK. That is what we should be aiming for perhaps, and then we can have all have the best for our children. Until that happens, the best education will be decided by a parent's ability to pay or where they live.