The above is reason enough to forget gun-toting teachers.
The only answer to more-secure schools in to spend money on perimeter security, access control, camera systems and properly trained security officers.
Penny-pinching catastrophes such as arming teachers will backfire so badly.
Could you take the test? Could you, if a teacher, and with all your experience, handle a school situation?
Let's say you are teaching geography to twenty 15yr olds in a classroom situated on the rear elevation of the main school building, with three double glazed waist-high windows looking out onto playing fields, one with a side-opener for fire-escape egress. The classroom entrance door opens into a long corridor which connects other classes as well as fire-escapes and on into the main building.
It is mid-morning. As you are teaching you hear three gun-type sounds from deep within the building. You stop to listen and then hear more gun-type noises together with distant calls and shouting. Your students look around, stir, start talking together and some make to stand up.
You can have any gun you like, and build on the above scenario if you wish.
Wanna havago? Go for it!
Exactly what will you do?