"In any case, we are seeing 'grammar' characteristics in schools just by their house prices alone. It's no coincidence that my dd's Primary school (the top Primary school in SATS results) abd who's Outstanding State Secondary school is in Top10 UK. So happens to be in the wealthiest villages who's 3bed houses are typically in the £600k+ price range"
So: are you saying that the SATS results are high because of the demography, which is children who live in expensive houses, probably with educated, aspirational parents (and the results simply represent the intake) , OR that the school is genuinely a marvel educationally and children are pushed beyond what is usual in other schools, so parents pay a premium to go there?
I realise of course that people do pay a premium to go to a school with 'top' results. IF the demography suits them.
However there are schools in Lambeth, in inner-inner-city areas where the FSM in primary is sky high (30-43%), the children enter with low base-line scores, and come out with averages above the national average and with very high VA scores. A school that does that is probably a very good school, with very good teaching. But those schools don't attract higher house prices (being in Zone 2 and near the tube does that all by itself).
My two closest comps in a 'less expensive' part of s London, with a v mixed demography, secondaries with mid-20s% FSM, are good comps. They get good results across all attainment bands.
I will say again I know London is different. I know there are huge areas where rural deprivation bites hard and whole LAs are declared not good enough by Ofsted (Norfolk, for example, I think), but my own belief is that it is better to address teaching and investment for every child in those areas rather than rescuing a tiny minority to a different building miles away and leaving the rest to rot.
London schools, on average, have higher stats that the rest of the country. The money per head in London schools is much higher that for outer London schools. I simply don't know how the spend per pupil pans out in Grammar schools, either in comparison to London schools, say, or other schools in their local neighbourhood. I have just had a whizz through the stats available on the DoEdn website and could only find the spend per head for Whitstable Community College - which has ...not good results... but not for any grammars in Kent.
Whitstable Community has roughly the same % of pupils with FSM as my DC's school, so presumably the same % of Pupil Premium income. The average teacher salary in my DC high performing comp is over £10k pa higher though. Even though I know the school uses a lot of NQTs.
So: maybe it I a matter of money. Put the money into schools where students need (and deserve) more support.