Smallman1 Millfield?
We used to turn them over year in, year out!
They’ve won the independent schools FA championship and appeared in the final a lot more than anyone.
Though tbf Ardingly have also won it 3 times which is still good.
Whitgift win the most tournaments prior to 6th form level, by which point a number of their pupils will have already turned professional and stopped playing for them.
https://en.m.wikipedia.org/wiki/Independent_Schools_Football_Association
Millfield are also way ahead of Ardingly in rugby (where Ardingly don’t register) , and seemingly cricket (though the cricket records are more difficult to find).
Plus Millfield was the most represented UK school at the London 2012 Olympic games. They’ve produced multiple Olympians “for every Games since 1956, making it the most prolific sporting talent factory on the schools circuit” (quote The Telegraph).
https://en.m.wikipedia.org/wiki/Independent_Schools_Football_Association
https://en.m.wikipedia.org/wiki/RFU_National_Schools_Cup
https://en.m.wikipedia.org/wiki/Millfield
https://www.telegraph.co.uk/education/2016/08/04/talent-factory-how-millfield-produces-more-olympians-than-any-ot/