Who may attend Catholic schools?

I'm all in favor of religious communities managing their own membership boundary lines -- a meaningful sense of belonging presumes a right to exclude -- but I'm having a hard time wrapping my head around the rationale behind removing the child of same-sex parents from Catholic school.  This story is generating the predictable left-right divisions within the blogosphere, and I don't have much interest in contributing on that front.  I'm more interested in what this says about the nature and mission of Catholic education.  I can see how tailoring the school's teaching to the preferences of parents might cause concern, but assuming that the school stays true to Church teaching, why would the presence of a child being raised by a same-sex couple cause a scandal?  And don't the kids who are not exposed to the Church's values at home have the most pressing need for the Catholic school's teaching?  

I did not attend Catholic school (nor do my kids), so I'm by no means an expert here -- is it common for kids to get kicked out of Catholic schools based on the conduct or lifestyles of their parents?  E.g., Are children of Mafia figures kicked out?  Have children of divorced and remarried parents been kicked out?  I don't intend these questions to be snarky or rhetorical -- the Church's witness on an issue that is so prone to reflexive accusations of mean-spirited discrimination requires consistent and principled policies.  Has the Church been consistent in deciding which children may attend Catholic schools?