There's a stage that's less drastic than violence, and that's yelling, "Get your hands off me!" Good and loud, as she was probably taught to do in Stranger Danger lessons, a few years ago. It will disrupt class and be massively embarrassing...it can be hard for a 13-year-old to stick to her guns hard enough that all the embarrassment sticks to the bully and not to her, but it really is all his fault.

That only works for unwanted touches. Unfortunately, there's not much middle school kids can do about being followed around by a classmate, when it happens in or around the school