If you look at the Sunday Times Parent Power top 500 State Schools, the superselectives are the top ones!
Altrincham Grammar School for Girls is defininately not superselective and is always in the top 5 but CVA > 1032-probably the best state school in the U.K
The boys' school in partially super-selective and has never reached these dizzy heights, don't know why? but one would assume has the same demographics but just more selective, my point being that just becuase a school is SS does not mean it is the best, and some SS schools e.g EB have brutal culling at 6th form to maintain league position, AGGS has hardly any students thrown out on their ear after GSCE. I have no daughters so no axe to grind! or children in the state sector.
"Students enter the school with well above average levels of attainment overall when compared to all schools nationally, although the school’s admission policy results in a lower than average attainment on entry when compared to most other grammar schools.
" my emphasis
from schools OFSTED report
The only other school I know that adds that kind of value to a childs education is The Grange in cheshire, I often regret not sending my boy there, but like most I was suduced by league tables!