When do you know it's time to fight?

I sadly report that my son age 16 is not in school at present time. My son suffers from mental illness, and was living in a Residential Treatment Facility. He completed a vast array of treatments, and was discharged home on New Years Eve. It was an amazing way to begin the New Year with my son home, and were pleased due to him being placed in what we believed was a great High School. I did have mixed feelings as the school the district placed my son in was less than welcoming, but hey my son is protected by law. He has mental issues, and IEP, and support services when not in school. Let me just say that the school had a tantrum, forced my son out of his placement. My son who was already enrolled in a school in Westchester County no longer has that school placement as an option, and the school he was assigned to ensured my son would not be allowed there. My son was told he "didn't fit" with the student body, that there was no space for him, that it wouldn't be fair to him to place him in a school where there was a great deal of "expectations". My son has NEVER been left back, he is in 11th grade, and has up until this Monday ZERO absences. Joshua is not ignorant, or dumb. He has a mental health issue that is being addressed outside of school. His IEP expressly states he is not a Special Education student, he has his credits, and passed his Regents. My son has more skills on how to handle himself than any other kid out there, as well as support services should the need arise. My son was belittled, shafted, and I feel treated in a discriminatory fashion. My son was essentially told that because of his IEP, he wasn't worthy of being in his placement school, and that they didn't want their school performance to be affected due to my son enrolling in their school. New York City Public School at it's finest.