Is it possible to sue my school?

The school I went to high school with currently has a no trespass order against me. Why? Because according to them I made threats on the last day of school and was a danger. I can promise you I am not. This was over a year ago and even after I was cleared by medical professionals they will not listen and will not ensure my return. Also the after I made "threats" I was dismissed back to class unescorted and they waited at least 30 minutes to even telephone the police. When the police did get there I was lead out in handcuffs which I feel is deformation of character as I was student rep. on the school council and I was a student trustee the year before. Also I am an Eagle Scout. In a letter to an ACLU they also made false claims about things I had said that degrade me even worse. Can I sue them? If so for what?