Here's a thought.
Currently, the practice is to either flee the school building (they call it evacuate) or shelter in place, depending on the threat.
If the building is on fire, they evacuate. If they're being fired upon, they shelter in place.
In the first instance, the danger is in the building, making it unsafe.
In the second instance, the danger is in the building, making it unsafe.
I think they are confused about when to "stand your ground".