Discipline

I wish there was a book that would cover this topic.  Not in a general context but specifically - for my boys.  That is one of the hardest parts of parenting.  I want to ensure that the appropriate consequences are imposed without going overboard.  How do I do that??  I guess we learn as we go.
I don't know what's gotten into my sweet Lincoln but on Friday he broke a kids necklace at school because the kid did something Lincoln didn't like and today he punched a kid that was being mean to him. We've done the writing a sorry note, he lost TV privileges last Friday and today he spent time in his room. I'm not sure what, if any of it will work.  He clearly didn't learn the lesson from Friday because he hit a kid today!
I have to admit on one hand I am a little happy that he's not afraid of kids and willing to stick up for himself but on the other hand I don't want him to be a bully and he knows he needs to use his words and tell his teachers.  I'm just hoping he gets this all out of his system now so we're not dealing with it when we're in kindergarten and grade school.  Oh what to do?!?!