As a student at a private school, you are there pursuant to a contract between your parent[s] and the school. The enrollment form they signed probably refers to a requirement that you abide by the student code of conduct (usually published in a school guide). As a part of that there is usually some form of "Due Process" hearing/procedure that they must follow before expelling a student for infractions of that code.
PA courts will generally accept a school's decision to expel a student if they followed the procedure laid down in the contract. The only exceptions would be if the school violated some constitutional or federal statute that concerns you, e.g. the Americans with Disabilities Act; other forms of discrimination by the school and the school takes federal funds (or is deemed to be a state agent in some other way). a greater review of the individual facts in your case would be necessary for such a determination.