Human reactions under dangers like this are extremely unpredictable. I mean, who has ever really had a chance to test the effectiveness or wisdom of their fight or flight response?

If there is a gunman I think you would want students spread out among their classrooms. If there's a major panic there can be deaths from the panic not to mention the danger of a gunman in a hallway as students try to escape.

I mean, there was a delay in sending out an alert, but you most certainly couldn't get very far if you tried to walk into the main group that morning.