Do NOT discuss this with anyone who works at the school. The pressure to be PC will always win out, and to cover their own asses, they cannot allow even the appearence of saying OK to having a gun on school grounds.
Your biggest concern is that someone finds out that you have ANYTHING to do with guns, and then they make a mountain of a mole hill and probably have your car searched.
When you say, "I want to keep a gun unloaded and locked in my car for a range trip after school"
, they hear, "I have a gun and want to bring it to school, and if the mood strikes me, I'll go on a columbine style shooting spree at lunch, opening the school to a mountain of law suits".
Lock it up in a box. Put it in the bottom of a duffle bag under some clothes. Put the bag in the least accessible place in your car and out of sight. Keep your mouth shut. Make sure your friend keeps his mouth shut too.
Oh, and don't forget to have fun while shooting.