Mind you, you called him a "Good Magician", good magician doesn't spoil some other magicians performance. If i were you, i would just get myself out of there before he do an exposure. He's not even worth of that word "Magician" or "Good", so the only way is to get away from him or do not perform in school, or do not perform near him. Last resort is to speak to him nicely ?, he's just an attention seeker guy and i believe he picked up magic to "pick up girls" and just get some attention. Nothing more than that, finally get some real nice effect and scare him away, some magic are "Magicians fooler".
Good luck bro