Why stop there? Fornication is a 10 commandment, why not let schools toss out kids who were born out of wedlock. Never ends.
How about being nice to people? Treating others well? That is what I think a true Christian does, but the meaning of Christianity is changing, it's becoming more a matter of judging others - not extending a hand.
That makes absolutely no sense. One, if those students were caught fornicating, they'd be tossed out of school, as Beach Bum mentioned earlier. Two, it's the fornicating, not the end result of that fornicating (the child) that the sin.
For all of your emotional arguments, you are dodging the simple fact that these girls violated the school rules, about which they were aware. They agree to abide by those standards but they broke them. That's why they got the boot.
Enforcing the rules and regulations is hardly a dereliction of Christian values. Where you equate "being nice to people" to lack of standard enforcement I'd like to know.
Let's just say that the students were merely suspended but allowed to return. That would be a form of mercy. Still, there'd be those who complain about that.