What kind of home life do most bullies have?

They tend to come from broken homes where they are under threat of abuse themselves. Bullying is the release of pent up anger etc on others who are less assertive or weaker.

In response to the above comment.

This is just not true. My child comes from a loving supportive 2 parent home. My sons principal told me her theory on why my son was behaving this way was that he is a small for his age child, and has been bullied before at school, but now has joined in to avoid it himself.

Children bully for all sorts of reasons. Dont think you can judge their homelife on it. Because you cant.