My guess is that the identity of the parents sexual orientation was not revealed to the school when the student was admitted.

And regarding discrimination... Maybe discrimination is discrimination in most cases, but i think its different in this situation. When it comes to the Catholic Church and homosexuality, what can you really say? This school is a private school, which believes strongly in a Christian God and the bible. I think it would be more of an injustice if the school was forced to readmit the student. Who are any of us to judge how a PRIVATE school picks its students?