The best bullet protection is the other people running around you.
It's quite the gambling investment hoping it will be a pistol round and not a rifle round your future shooter will be using.
Only a matter of time until co workers notice your new piece of costume and bring it up to the chain of command.
If using the magical clip board, where would you hold it? In front of your face, center mass, or pelvic girdle?
Do you have the balls to just stand still in front of a shooter while holding your magical clipboard or backpack? Instead of running, flailing your hands like you've just walked into a spider web? 100 percent of unarmed people wouldn't.
If I were a teacher/work in a school environment, my time would be spent on learning to be the best room barricade specialist known to mankind. That is if you're lucky enough to have a room with doors.
I would figure out what desks, chairs, furniture, etc... Can be lined up in a row behind the door to the wall across the room to keep the door from being pushed open. Then I would clearly lable those pieces 1,2,3,etc... On the top, indicating which piece goes first against the door, second piece behind that, etc... Ideally, the last number would be the piece closest to the far wall. The less thinking you do have to do under stress, the better.
Active shooters like to be active. They're not going to spend much time, if any, when they encounter some physical resistance like blocked or closed entryways. They'll move on to the next available area.
I'd have on hand a few cheap rubber door stops or invest in a few well built "tactical" door wedges.
Good luck.
So I was talking to my wife about this since she is a teacher and she said All of the doors at her school open Out into the hallway.