Son with 504 suffers from anixiety and depression as a result of bullying . He was detailed and Expelled partially for his behavior from this

The school must do a manifestation determination - that means there has to be a meeting and determination that your son's behvaior is not a manifestation of his disability.  If this has not been done, ask the school to do it.  You may be better off with an IEP - Indivdual Education Plan - instead of a 504 - but that will depend on what is happening with your son.