When I was young, I learned from 'experienced' elders, that if they came at you with a knife, you run away, but if they have a gun, you charge them because you can't out run a bullet.
I live less than 5 miles from that school and have followed the local news most of the day. The perp was taken down by an assistant principal AND a student! One of the wounded was a boy who stepped in front of some girls the perp was going after.
The entire event from start to finish lasted only a couple of minutes as the perp ran down a crowded hall slashing and stabbing as he went. It all happened very fast. Some of the wounded kids never even saw the kid coming and he stuck them in the back.
Also talked to a woman who knows the kid and his family. She said he and his family are nice people and she is mystified as to what drove the kid to do this.
But the bottom line is that there were kids and adults who showed courage in the midst of a very confusing and fast evolving situation. They stood up and probably saved some lives. They weren't the sheep that you imply.
That kid is a hero too. He's a sheepdog. He probably didn't even think about it first.