I hate to tell all of you this... but when my oldest started school, I had the same problem. Back then, he was my first and only child. I was raising him to be "nice". I taught him that fighting was not acceptable in any way, shape or form. Boy oh boy did I sit up some nights and regret those 5 years of guidance. Those boys on the bus picked on him because they knew he was peaceful and nice. When the bus system did nothing about it and the school system did nothing..
I told him.. if they push you again or if they make you feel scared, punch one of them. I told him that he needed to hit one of them ONCE and they would all back off. He couldn't do it. Week after week he would get off the bus crying. I wanted and wished that I could BE him for one day and make all of those kids stop hurting my son.
Finally, one day...the school called ME! My son had laid a punch on one of the boys on the bus and they needed ME to come in for a conference with the other parent!! My timid, shy son hits someone and THEN they do something?? Wow!
So, we had the conference. The principal knew how non violent my son was (is). He said that he didn't even want to have this conference because he knew what had been going on. The parent of the bully was just as much of a bully (at first).
She started yelling at me. In the most monotone, flat voice I could muster, I said "Your son has been bullying my son for three months. He had it coming." She looked shocked. Her child started crying. She asked him a few questions and he finally admitted it.
He had been lying. apparently when he had been questioned in the past about bullying my child, he said that he was NOT bullying him. When my son was asked if he punched the kid, he admitted it. Yes, another value we hold dear is truth, even if it's uncomfortable for you. So, because they took the other kids word for it for those three months, he had never gotten in trouble. This is why it had taken the admin so long to DO something.
One good thing did come of it. The other kids finally saw that my son *might* get up and hit them (which to this day, he tells me was the worst feeling in the world, he felt bad the minute he did it). He has had no other fights because of it due to his ability to carry himself, knowing that he can and will if needed. It's 12 years later and I am sure things are a bit different, but still. A karate class here or there probably would have the same result. It all boils down to your nice child having some courage inside. Just in the way he carries himself.
I've raised my younger child much different. With the same values and he knows the rules. Same as his brother.. no hitting no fighting, treat people the way you would like to be treated. But with an amendment: You can hit someone if they hit you first. My youngest has never come home from a fight. He's never come home with dirt all over him from being pushed into the grass at the bus stop. It's because he has that inner confidence and he carries himself that way. My older child stopped being picked on and he has plenty of friends too. That one punch changed his life.
Kids are cruel, but even the bullies are still just kids and just as scared as the children they are picking on.