Do nothing isn't the right approach, but children do need to learn how to deal with the bullies they'll meet in life - I know, I was bullied terribly when I was younger. Could my parents have intervened? I dunno. I don't think it would have helped, other than they could have reinforced my own feelings of self-worth, something they didn't seem capable of doing. Make sure your son knows he's valuable, he's loved and wanted, no matter what the rest of the world may be telling him right now. Poor little guy.
This sounds as though it's gone past the 'let them work it out' stage. The school should definitely be doing more to stop this. And you, Mom, need to step up to the plate and make them do what they need to do. No one else is going to do it for you. Figure it out, get to that school, be an active advocate for your son. I don't know why the courts are involved in your life, but you may be able to get someone in the court system to help you with the school, if they are unresponsive.
ETA I do think children need to be taught to take care of themselves - the world isn't going to coddle them when they get out into the real one, and too many kids nowadays are raised to think the world revolves around them, it's a far fall when the cold, wet hand of reality hits them.
