Statistics giving detailed breakdowns of the medals issued annually by schools are hard to come by. The only available source, that I know of, can be found in the programmes for the Prize Giving Ceremonies and/or Concerts held by all schools. Of course, the survival rate for these ephemeral items is very low.
If you know the location of any similar items, in school archives or local museums, please let me know.
I have created PDFs for a series of such programmes from three London schools.