If he's not for sale, then that should be the end of the matter.
One thing that has occured to me - is it not illegal for school children to be bound by professional contracts?
Like Mike said, people got annoyed at clubs just saying no and refusing to sell young players so they changed the system to allow you to sign them but for much greater prices. You either get them quickly before they sign pre-contracts or you attempt to fight out a decent deal for yourself.