I went to a Catholic school for Elementary, Middle, a Jesuit run high school, and a 'Christian' University. So I've gone to 'religious institutions' my entire life. They aren't the same.
It was a tradition at one time in a lot of Catholic families that at least one child in the family would grow up to become a priest or a nun. As a result, a lot of people got pushed by their families into the clergy that never wanted to be there. This is why there were so many mean old nuns and priests - bitter, miserable people who hated how their lives turned out and took it out on everyone else. That kind of stuff is pretty uncommon these days, and people enter the clergy because they want to. The priests and nuns that taught at my high school and college were all nice, well-adjusted people for the most part. It wasn't like that in my mother's day at Catholic school, however.
I really can't see this kind of thing happening in a Catholic high school these days. One of the girls our senior year got pregnant, and while of course we were all taught to be celibant, the faculty was completely supportive of her. There were no openly gay students in our class, but I don't think they would have expelled anyone for being gay either.