Not an exceptional event at all. Actually quite common. The school has an officer on site who is also threatened frequently, along with teachers. Been to a high risk school lately? It is never the kids fault!
And yes, if there are no consequences to actions, then why would anyone obey the rules. So yes, while unfortunate the "one" pregnant girl will likely fail in my model, I'm not so sure she will succeed in yours either. After high school exactly what are the odds of a single mother succeeding in today's world?