I'm so sorry this has happened to your son. But I don't think hitting back is the answer. I mean he should know if he "needs" to defend himself he can (i.e. if he is ever in a more than one on one situation) but in situations like this he did the right thing.

My little brother had almost an identical situation happen to him a couple of times as a kid (one time he was only passing on a message from the boys mother!). He didn't fight back, he just turned away and walked home. As an adult now, he is not violent at all, and is very good at dealing with all sorts of confronting situations in a mature manner way beyond his 22 years.

Me on the other hand, well, when my brother came home and told me what had happened. I walked down to the sports centre, saw that not only were there boys of his age there but also boys from my class. I got right in the little (read: taller than me at the time LOL) *h*t's face and told him that if he ever went near my brother again, god help him! I then turned to the boys of my age and told them they should all be ashamed of themselves for just standing there when this happened and that no girl in their right mind would want such pussies so they were no longer to speak to my friends and I. (so mature, so mature!) But now, as an adult, I am not good at dealing with conflict without resorting to profanities and violence of some sort LOL!

It is good that the school is acting on it and suspending the other boy. Because your son didn't retaliate, the staff will look out for him I'm sure. But can TOTALLY see why you're seeing red!