We had several experience that might help.
1) my daughter was in third grade. she has always been a "toothpick with hinges." She was tall, but skinny, skinny, & her best friend was a foot shorter than her. She & her girlfriend were having difficulty with a fith grader who was a head taller than mine, & built like a tank. Cleary could take the 2 out without any trouble. However, when my daughter & I talked about it, i explained the concept of self oesteem. what you think of your self, how you see yourself in the world around you, & about how much power that you perceive that you have.
If this kid was secure in himself, he would not have to pick on girls half his size, he'd pick on the kids his own age. He was using the girls to make himself feel, look bigger than he does. It's not about her or her friend. This made perfect sense to her. The next day she came home from school, her head held extremely high, chest out, obviously feeling on top of the world instead of beaten down. I asked "What happened?"
That bully got in Amber's face, so I got in his. I told him "you must not think very much of yourself if you have to pick on girls half your size to feel good about your self!" The kid took a step backwards, looked at her cross eyed, & NEVER bothered her again. The amazing thing about this encounter really was what that experience did for her. There wasn't a kid alive who could get away with bullying her or her little brother.
My son's experience was a little rougher, because after all you're not supposed to hit girls, but boys treat boys a little different. A confrontation is as likely to end in a fist fight. When my son was little he was a hitter. He could not talk til he was 3 but found "sign language" and biting to be effective ways to get what he wanted momentarily. Eventually I had to give my daughter permission to "teach" him that it doesn't feel good, so after she had to "hit him back" once or twice, he finally quit. "It's not OK to hit" finally got through. His first encounter with a bully his sister was present, & she "took care of him" with her words. When we talked about it later, i let her know that the bully will come back for Ashton, because a girl fought his battle, & although it's good to stick up for one another, boys must defend themselves to have a place in their world. So the bully did come back for him. Knowing it wasn't OK to hit, meant he had to run. Seeing that he was loosing this, he ducked, & crunched just as the kid was getting to him, causing the kid to trip over him, & splatter, then he ran home. At this time we called the police, & the other kid was put on a restraining order from the playground. He saw him a couple of times, but only from a distance, & the kid left him alone.
Name calling was another issue big one. What helped my son here was a perception change. (2nd or 3rd grade) Really, ultimately, do you care what they think? You need to care what you teachers think, or your pastor, or you parents. We will give you feedback to who you really are as a person. Don't let these guys define who you are. Often name calling is to get a rise out of you. If you don't react, they will quit. It eventually did. But the other thing that it did for him was to create an immunity to peer pressure. Later in Middle school his best friend mother told me... the thing I admire about your son is that he just doesn't give a rip about what the other kids think of him, & isn't in the slightest swayed to do something that someone else tries to pressure him into. He's not afraid to just be himself, & if someone doesn't like it, it's their problem. My favorite book on child rearing was "DR Sears, Guide to parenting", LOTS of helpful information about development & stages & creative ways to handle stuff. He's a physician & child psychologist.
Last thought, I heard Dr Laura recently. (although I don't agree with her all the time, this might also be helpful)
Her way of dealing with childhood dissensions is to invite the other kids (who are behaving badly) over for pizza, movies, to a park for a picnic, or something. It's harder to hate someone when they invite you into their world. I never tried this, so I don't know.
Hope this helps, May God bless you!
Ang