Very valid, and has doubtless happened. Losers have the most ingenious tales to cover their actual deeds. (Why no, I was not cheating, I merely was checking to see how far along the other students are in the exam to see if I was going fast enough.)
Also valid IMO, this kid could have done other things besides bring a gun to school. My suggestion would be to wait on the spot for a parent to come and leave the weapon with them. (Late to school? OK, parent can give an excuse for this.)
See, now THAT is an EXCELLENT scenario -- the kid does the right thing and even gets to be late for school!