S.D.
Hi E.,
This is such a difficult issue! Dad's say let them handle it, us mom's want to "protect" and the school says no fighting ~ which includes fighting back, which unfortunately is often the only thing that makes a bully back off.
This is what I did, when my son was in 1st - 2nd grade. I let the teacher AND principal know what was going on and let them know without a doubt, that I was not going to allow this to continue. We talked with our son about avoiding potential situations and to keep quiet. If he was confronted, to go to a teacher immediately.
When that didn't work, I had no choice but to allow my husband to "have his way"...we then told our son that if the bully shoved/hit him again to hit him back as hard as he could. We also let him know that he'd more than likely be expelled from school for fighting and it'd be in his permanent record. I then went to the school and let them know that we'd given our son permission to hit back because they hadn't resolved the problem. (By the way, this was off and on over the course of two school years.) Nothing ever happened after that. I think just knowing he wasn't going to get in trouble from us if he had to fight gave our son whatever it was he needed to avoid the confrontations. In fact, his 3rd grade year, they became friends.
If you don't like that solution, and the school doesn't take the required action for the bullying to stop, let them know you're going to file a police report if it happens again. And ask them to relay that information to the bully and his parents as well. If you know the parents and believe it would be like talking to a brick wall, definitely don't try to reason with them, let the school handle them.
Hope this helps, I know it's not the most "politically correct" way of dealing with this situation, but we were truly at a loss when the school couldn't/didn't stop the bullying.
Good luck!
S.