I understand what you are saying, as this is what that majority of Christians I grew up around believe as well.
What troubles me is, the standards are set only when the sin is visible.
For instance, in our school, the two students who had an abortion? They could come back to school. But not a girl who was visibly pregnant. As long as it didn't show, they could be there.
So how all the teens who are engaging in sexual behaviors or full-on sex, but just haven't gotten caught because there wasn't a pregnancy? I'm thinking of an instance at my former school in which a teacher intercepted a note from one student to the other describing their planned weekend rendezvous.
Or the teenage boy (though to be fair, it could be a boy OR a girl) participating in various behaviors while watching porn on their phone or computer? How about the teens who are sexting back and forth?
Being taught Christian standards is one thing.
Living them out is another.
How do we decide which who become the scapegoats and public examples, and who do not?
Because then the message becomes, "As long as you don't get caught or show any public signs of sinning, you are acceptable within the student body."