I agree with Greenmousa. When I was a kid "tattling" or "running to the teacher," or "telling your parents" garnered very little respect from your peers, and usually led to further escalations on the part of the bully: "So, you went and told on me, hu?"
Not to say that I never asked for help, or let my parents or teachers know. On the contrary, in my day and age, unless the other kid was weilding a knife or lead pipe or it was six kids to one, most advice was centered on how to deal with the situation on your own.
Violence isn't always the answer. Since your brother is not bulling other kids, it is highly probable that he is much smarter than the mentioned scoundrel. I called out a few bullies in front of their peers, girls, etc., letting them know that the only reason they are acting like such a dick is to try and climb up upon someone else's percived smallness. The other kids should also be told that if he wasn't pestering your brother, it would probably be one of them. It doesn't take long for a group of kids to see the reasoning behind this type of exposition, and most will fall behind your bro. It takes as much balls to lay it on the line like this, in front of others, as it does to throw a punch. Besides, cute girls (and the smart ones, too) find these types of actions very attractive.
The worst that can happen with the aforementoined scenario is that the bully gets so mad/feels so threatened that he takes a poke at your brother. Win or lose, the kids around will see your brother as the bigger person.