A lesson for all school kids too. If there's a shooter in the school, get the hell out! Throw a chair through a window if you have to, but get out! Stupid cops couldn't even peek in the windows where the shooter was? Chicken [bleep] cowards.
I've been telling my kids for years, if there's a shooter time is your friend. Space buys time. Grab a fire extinguisher and head for a room with a window and a door you can lock.
Fire extinguishers are good for busting windows and can lay down cover. If the shooter closes in they can powder him and make more space or fug him up.
Whatever you do.... don't wait to get shot.