While I firmly believe that every now and then, somebody deserves a beat-down, it is rarely the best first option. There seems to be a lot of assumption here. But there are things that you should do to make sure if there is any trouble that you have covered your bases and have made an attempt to resolve the issue peacefully.
1) Most important. Make sure the school is aware of it. Bullying is a BIG no-no these days and schools are getting in trouble for it. Lawsuits and loss of Federal Aid are serious motivators.
2) Talk to the kid's parents. If they are decent folks, they'll be humiliated that their child is doing this and it will stop. If they are not decent and think, "boys will be boys", then tell them that your lawyer is a boy and hope they have one too, because you are going to involve the law and the courts. Maybe even sue them for negligence and child endangerment. Involving the law and the courts costs something that few parents can spare, time and money. Nothing restores sanity like having to pay money for something that could be solved by basic human decency. Don't bring your kid along. Maybe they will be friends but why would you want your kid to be friends with a bully?
3) Most importantly, talk to your kid. Tell him his options. Maybe hang with friends that don't hang with the other kid. Maybe learn to fight or even debate. Have him tell the other kid that he's a bully and he's going to report him as so. Sometimes when you're outsized, the only option is to run. There's no one solution. But also tell him that, later in life, he's going to meet a lot of jerks just like that kid, but grown up, whose hostility will manifest in every possible scenario from a jerk boss, to angry cops, that clerk at the DMV who won't process your claim, that pimple-face kid that spits in your hamburger, etc.. How he learns to deal with this kid now will help him grow and deal with life in the future.
On a side note, I was a victim of a bully in 6th grade. One time, after he pushed me a few times in the crowded hallway, I said, just loud enough that other's could hear me, "It's OK if you are gay, but I'm not, so NO you can't blow me!" Some kids nervously laughed while some pretended not to hear me. After that, he never even spoke to me (for four years!), never mind push me. (I wonder if that outing would be considered bullying today?)