I don't get it. He turned it in to the teacher - it's not like he was trying to get away with it. He could have shotgunned it in the bathroom and had a small chance of getting caught. I'm OK with teaching that actions have consequences, even mistakes, but three day suspension and two months of alternative school? Pretty over the top if it really was a mistake.
Now if they had caught him shotgunning it in the bathroom, that's another matter.