Hmmm. You may be on to something here.
Frankly, I'm not enthusiastic about arming the teachers. I've met a lot of them, and didn't entrust my kid to their care. Never mind, trust them to carry safely around my kid (or anyone else's, for that matter).
But the concept of a simple door bar should be easy enough for even the dimmest of them to grasp.
And when a bad guy gets on the wrong side of the door?
(And I agree, I’m not keen on arming more government employees—er, teachers—though having someone there with the ability to defend could be worthwhile.
Actually this is a great idea and an example of better is the enemy of good enough. Since classroom doors in my experience open in to allow hallway passing it would be easy to anchor two stout hooks on either side of the door and provide a steel bar to drop into them. Relatively inexpensive and would be unobtrusive. They could be installed by the school’s custodial staff during one weekend.