One

This is a great book for teaching kids to stand up for one another.  It is about the role of the bystander.  When kids stand by and watch other kids get bullied, they are as culpable as the person doing the bullying behavior.  (I try to avoid using the word bully)  It is very harmful to their self esteem to watch and not help.  Lots of people have stories from their past about someone they wish they had stood up for, and they are very sorry that they didn't.