Need help please. Son is being unduly harrassed at school.?

-My son's girlfriend had an argument with this girl. The girl then went to the guidance counselor and told her that my son was beating on her (his girlfriend) meanwhile bragging on FB how she was going to ruin his girlfriend's world. Well it has rocked mine, I tell you! My son was brought in and harrassed by the campus police, without me being called, the girlfriend has been brought in on numerous occassions being asked if he has hit her. ok I would want someone being abused to be protected, but this has however been going on for almost 4 months now. All the teachers look at my son like he is an abuser. I know he is not. In fact because he is a teenage boy, the only time they are not with my supervision is when they are at school. I know my son and know he would never hit her. I spoke with the principal in the beginning and he stated to me that it would die down, girls were into strating trouble but woould soon move on. The girl is no longer the problem, now it is the teaching staff. What can I do?I would kick the **** out the teacher...or sick your son on them :D
put him in a different school