I personally don't see anything wrong with keeping it in your car locked in the glove box. Unless they do random sweeps of cars (which is probably not allowed) it's unlikely they'll ever find it. Biggest thing is don't be stupid, people get in trouble for bragging about carrying a knife or having a knife in their car. If you don't say anything about it, chances are you'll never have a problem. But bringing it into school is a good way to get in trouble, especially in a place with really strict 0 tolerance policies.