We applied for 2 banded comprehensives in different boroughs - they don't tell you what band you are in until the letter comes after allocation day.
@Araminta1003 I do agree with you that very high performing children and those with associated SEN need the right support, like everyone else.
My maths- orientated Dc was not 'off the scale' like your DS, but did get 9 at GCSE, A* at A level and top marks in Further maths . The top mathematicians were always in teams and clubs preparing to compete in various national maths competitions, they did STEM competitions (and beat top private schools to win regional heats) etc.
As I said before both London comps my DC had experience of were hugely diverse in terms of all social factors and attainment levels. Gang members present etc. There was never any bullying about being clever - there was acknowledgement that the clever kids were clever. And one of my Dc is very weedy, and musical, and has a discernible physical disability.
The phrase 'he will be eaten alive' was used on MN a lot by parents of similar kids - he was never even nibbled.
Young people like your DS need the right support. Whether that means the whole school structure has to create separate buildings and institutions and divide kids out at 10 etc, I am not convinced. Certain schools (comprehensives) could have 'super sets' with places open to genius mathematicians (it is usually the maths students) for example. Or classes conducted over Zoom with similar students form other schools. In fact that would enable all schools to offer minority interest courses such as Latin / Mandarin or whatever.
We need to be innovative, flexible open and creative about how to educate, rather than just harp backwards and forwards between old models. We are nearly a quarter of the way into C21st for heavens sake.