There are things that a child who is being bullied can do to try to stop from being bullied. The child must understand that any aggressive behavior that he exhibits will just fuel the bully's behavior. So, as frustrated as your child gets, he must learn to self-regulate his aggression. This is not easy, but if you teach him self-talk, he will have a method with which to use to diffuse his own anger and frustration.
On the other hand, if he behaves in an assertive way instead of behaving in an aggressive way and tells the bully to "Stop hitting me, or stop pushing me, etc.," the bully may indeed stop. Also, see if your child can have another child nearby when he walks down the hall, for example. Often, bystanders are a good deterrent to bullying.