You need to go to the principal immediately. I work at a school and if something like this was going on, my principal would want to know before anyone else. I would tell the principal exactly what you said here, that many students are afraid to come to an adult about this bully in fear that they will later be picked on or hurt. You could also suggest that you don't want your son to be singled out as identifying the bully because he too is afraid of later being bullied. There are many ways to get to the bottom of this. Schools are very concerned now with the act of bullying, so I'm sure there will be a way to get to the bottom of this in confidentiality for all of the students who have been victims or are afraid of becoming a victim to this bully.

Something like this needs to be addressed not only for the victims, but for the bully too. It is when the school system and parents let this behavior continue in an individual that really hurts society in the long run. The bully may be able to be reached and helped so that this behavior discontinues and that person will live a happier life too.