That is so much modernist quasi-Catholic BS out of the head of the school. That gay partnership is public and scandalous. A divorced and re-married person without an annulment would fall into the same category, but not the divorced chaste parent. The practicing contraceptor is not a public act or scandal, therefore different.
When the classmates want to go to the gay parent's house to play or spend the night that puts Catholic heterosexual parents in a real quandry. No one with half a brain wants that kind of modeling for their child and to explain why they won't let them go presents a problem for both children.
It is unloving for the school to do this, both to the homosexuals, the straight parents and all the kids. The truth done in love will set them free.
Well that. You should teach theology to those that pretend to run that "Catholic" school.