A lot of Catholic schools in Philadelphia have many students from single mom homes that are not Catholic. They provide a place of refuge from both the neighborhood and the public schools; certainly a Christian calling. The schools realize that they may turn a few kids to Christ, too.
So?
Really, So?
Theu knew beforehand their lifestyle was against the rules the school was run by, and they chose to ignore those rules.
By ignoring the rules of the school they decided they were better then the school.
The school decided they weren't.
Catholic schools don't make such rules about who might attend.