PA has a religious exemption (which can be whatever, you do not need to explain yourself or be part of an organized religion). There is no specific exemption form. Most people just write up a letter which parrots the wording of the exemption law. I don't remember if it has to be notarized or not, but you don't need an attorney. I have no idea how private schools work, though. I would guess if it's an alternative school, like montessori or waldorf, they would be much more likely to work with you. Good luck!