You can judge something like this the same way you can judge whether or not a kid is old enough to babysit: In hindsight. Did anything bad happen? No? Good! Then he was old enough, congratulations.

The title is: "How to stay safe in a mass shooting." That, frankly, is stupid. If someone is trying to kill you, you cannot "stay" safe; you are already in grave danger, and you need to act immediately. The better title: "How to react when someone is trying to murder you." If you can run away in complete safety,…