Too much of what we do, or are required to do, is driven by financial considerations. A lot is also driven by the fact that education has become highly politicised - ideas are introduced as being "Tory" or "SNP" or whatever, rather than just being ideas. Too many politicians have no idea about teaching (or even children - those that have children often have them in the best schools and have the children that are very likely to be high achievers).
Much more of what we do needs to be based on proper research, peer reviewed, tested within the system it is intended for.
Much of the arguing on here has centred around Maths. There may well be very different evidence for best practice in Maths, from in English, or MFL or PE. But we don't always know this and, even where we do, much of the interventions themselves are driven by ideology, or, money.
For example, I was encouraged to use a set of computerised reading tests sold by a company as "Accelerated Reader" - essentially quizzes about books pupils had read. It attempted to Band books by difficulty and length, awarding points. It cost £££ and was backed up by research from Dundee University. I was working towards an MEd (and this was a while ago so my recollection does not include names, sources etc - these are all stored on my computer, not my phone) so I did a lot of digging.
The company was researched by the company owner's brother-in-law. One frequently cited piece of research was in the US and it was unethical (children were named) small scale and written by someone with a very limited and suspect bibliography.
Yet, budgets had been spent on this scheme.
Equally, "Brain Gym" and, more recently "Learning Styles - kinaesthetic, visual etc" have been debunked after schools and LEAs spent huge amounts of time and money on buying them in or training teachers to use them.
We have just (not me, but my school) spent a fortune on "Tree of Knowledge" a private company of motivational speakers. Yay! Wow! It was great! But no one measures the actual effect of the "intervention. " Even my cynical assumption, based on those who were promoting it, that it was crap has no foundation in actual evidence - just my opinion.
So, if you ask what is best for the top 1%. Who knows? They are often already in private schools being paid for, on scholarships, in grammar schools etc. So any evidence is already skewed by the system.
DS is by any measure top 1% and he is off to Oxford. He got there (1st ever) from a tiny school with entirely mixed ability in all subjects until the end of S3 and then 3 years of subject levels allowing for some separation. He did very, very well. Could he have done better? Probably. He certainly has the odd B grade that could have been an A. Would he have done worse, however? A highly selective school might have screened him out, or he might have just missed top sets, or he might have flown higher.
Who knows?
Someone told me recently that the 2 things pupils value most in teachers ( again, no reference to the research, trust the speaker, you don't have to) are KINDNESS - i.e. They want a nice person who cares. And ORGANISATION - they want someone who can keep things running. My instinct is that the 2nd of these, in abundance, backed up by the school and parents means that mixed ability can work in some classrooms. Is it best for all, or even the majority. Again, who knows.