May being the operative word here. They might instead find that while searching said teacher for a gun that another teacher that actually has one meanwhile has snuck up behind him. It's a crap shoot for sure. One that not many people will take if they don't know what the odds are actually. Again - crazy people don't care about odds.
Think about it - you are flying down the highway well above the speed limit and you see a cop car at the side of the road. Do you hit the brakes hoping he didn't have you on radar already? Most people that are paying attention would. So as you drive by said police car on the side of the road and see that it's empty - just a decoy - you are relieved that you won't get a ticket, but you still slowed down anyway. Now, this only works once. Same spot on the same highway the next day you might fly by that cop car knowing that it was vacant yesterday. Same thing the next day and the next. Until one day that the cop is actually in the car and pulls you for speeding right by and not slowing down one bit. This is how deterrence works. You stay in line because you don't know if you are being watched, if your going to get pulled over, if the person you are picking a fight with is actually better prepared/better trained/better/stronger/faster.
Think about this on a global scale as well. Russia has always had us by the throat with the threat of nuclear war. The big bad bomb and the threat of mutually assured destruction has had both sides at bay for decades now. Now that Russia is all the sudden hungry for expansion into neighboring areas, some have folded where Ukraine stood and fought what most would consider a losing battle. Out gunned, out manned and out numbered by military vehicles, they stood their ground and fought back. The fact that it has taken this long to win so little is pretty telling. I grew up thinking that one day "Red Dawn" would come true and that Russians would paratroop in and take over the country from the inside. Now, it seems as though they can't even roll into a neighboring country and take over by force, let alone a country on the other side of the world. But yet, the nuclear threat still remains, and so the U.S. has been relatively hands-off.