"Just as The Royal Ballet School is the place for the exceptional ballet dancer."
Not Tring, Hammond, Elmhurst? Or any of the schools that teach from 16+, usually taking students from non-vocational schools but from which some graduates go on to ballet companies (e.g. Northern Ballet, English National Ballet etc)?
I think the point I am making is that dance schools select at different points, acknowledgeing that a child who at 11 might not have been White Lodge material might well develop to be suitable for 16+ entry, even though that child would only have been at a daily 'after school' type non-vocational dance school for the intervening 5 years. [DD is the dancer in our family]
Equally, in academic subjects, I might say that the 'super-selective' type academic experience totally wrong for DS at 7 and definitely a second best at 11 might be absolutely perfect at 16+. Or it might be that he continues a 'non-selective' school environment until 18 but chooses a highly selective university. Or not.
Very able children, like all other children, are people. Not just their ability. We all, as parents, have to choose the best option for that 'person', not for 'that ability alone.
I don't think we should 'fetishise' a single school, or type of school, as being 'always the best option' for exceptionally able children. For some, the best option will be selective private, for others selective state, for others comprehensive state. It will depend on the individual as a whole, and the values of the family, which is 'the best' option for each individual. Information like the IMO tables [scary - didn't realise that iI knew half the team in 'my' year] show that very, very high attainment is possible from all school types.