My take on the point mooted in the middle of the thread - about some schools being able to deliver way and above the curriculum - would be this:
Most independents and selective state schools, as well as many comprehensives, do deliver an education which goes beyond the curriculum/the minimum/just results because, quite simply, the children they have are much easier to teach the curriculum/exam syllabi to and so they have more time and energy left to deliver other things.
Sure, the independents also have the facilities (not in ds's school's case - their facilities are not as good as many of the local state schools, but then he's not there for the facilities), the extra money and, in the case of the very best schools in both sectors, their pick of excellent staff. But I think you can't overlook the different levels of energy, commitment and resources required to get good 'results' out of one cohort compared to another, making it nigh on impossible for some schools to provide anything like the same kind of overall experience.
It's like when the specialist schools idea first happened. Overwhelmingly, in our county, the 'best' schools with the best results were the first to choose a specialism with the attendant extra funding. As one of their Heads was heard to say, it was quite easy for them to dedicate time and effort to put in their specialism application when they didn't have discipline, learning and high staff turnover issues to concentrate on.