How would you punish your 3rd grader for threatening a kindergartener with a knife on the school bus?

I would be in full support of the school if they wanted to expel him. Definitely a suspension from school would be in order. If they took him off the bus permanently, I would support that as well. I would also (obviously) confie the knife and search his room for any other such items. He would definitely be sat down and we would both (his father and I) have a discussion about the situation. However, I'm betting that the home he comes from is nothing like mine, where we have taught our children from very small how they are to treat other people, first expecting them to treat their siblings in a right manner and going from there. Some parents really don't teach that, and if there is violence in the home, that is where he learned it. But if it were my child, he would also be grounded to his room for at least a week. And he would be driven over to that other boy's house with both of us present (me and his dad) and apologize formally to the child and sincerely.