This shooter shot through the glass classroom windows in the door.
Remember though. someone set off the fire alarm so that kids would be in the halls like sitting ducks.
If you flatten yourself on the wall with the door, he can’t see you. I remember all the glass in my schools having screen in them, so they wouldn’t shatter, so I’m thinking a shooter couldn’t break the glass and then reach in to open the door. Good chance to twist his arm off, otherwise.