I admit right away that I haven't read very much in the area of appropriate response to bullying in school. What I do know is from experience, and most of my experience consists of the parents of kids who have bullied mine complaining of how much their kids have been bullied!
It seems to me that on the parents' side, the first thing you need to do is admit that there are no bullies, just bullying behavior, and that all kids do it to some degree. It's up to adults to model and teach right from wrong in how you treat those around you.
Also, once you call a kid a bully, he becomes a bully. Kids respond to the labels you give them, and it becomes self-fulfilling.
What are your experiences with how schools have responded to bullying?