Merlin question

It's about a boy who lives in a castle, his best friend is becoming a knight and it doesn't look like hell become one himself. Finally a wizard appears at court and when the boy leaves he follows him asking him to take him to a school for wizards. The wizard takes him and he begins his studies but he's not very good. When he joins the school he's told he cannot wield a weapon again. As the story goes on he becomes better and at the end he is tricked in to helping a teacher summon a demon and the only way to stop him is to wield a weapon. This means he saves everyone but has to go on a mission to be allowed to wield magic again.