I would make sure the school was taking some action like putting him on a probation of some sort. I would not be happy and I would let the school know it would not be tolerated.

I think it depends on what he was yelling about in a way it could be good for  kids to see that even adults get Angry and that you have to apologies. It also shows them that bad things do happen. they should also understand that they shouldn't just go around yelling. ( not that I'm saying anyone should) although I think it is inappropriate for a teacher someone your kids and I should look up to to be yelling at the top of his lungs at others. Another thing I find is that if it was for good reason the kids should also see that problems should be confronted. Instead of worrying over this I think you should use it to teach your child that there are other ways to confront that by explaining it then pointing out the faults the teacher made.

Hope that helped not very good at the whole grammer and stuff so disregard that