Try to make sure the school has good links with professional clubs. A good bit of research to do to find strong footballing clubs is to look which schools professional players in your area went to. For example if you are from Birmingham city in the UK, it might be worth seeing where the local professional players that came through the academy went to. By trying to get yourself into these schools you at least know that the school has good links with the professional academy and the school has released those players to that academy for training etc.