In theory it doesn't sound bad, but getting administrations, dept of Ed, etc. involved it will end up with a gun locked in a container, possibly in the room, or maybe the office, and the particular teacher would then need to leave their current location, move to the "arms cache", engage the threat, and so on. i think there are better ways.
For one, just allow those who CC to do so on school property.
For one, just allow those who CC to do so on school property.