See...here's the problem with this question - unless the person carrying the gun has been through military or police training, it's incredibly unlikely that anybody carrying a gun in the class would be able to make a difference.
It all has to do with brain chemistry. Your brain has three basic parts: the reptile brain, which deals with automatic functions (breathing, heartbeat, etc.), your mammalian brain, which handles instinct and the "fight or flight" response, and the higher brain, which handles thinking and logical thought. Because the higher brain is slower to react, when adrenaline starts pumping in an survival situation, your higher brain shuts down and the mammalian brain wakes up and takes over.
If you've been through military or police training, all their firearms training is exactly about training the mammalian brain in what to do. So, once the higher brain shuts down, the mammalian brain knows how to aim and use a gun, etc. If you haven't been through this training, all the information on how to aim and use a gun is stored in your higher, logical brain...the part that just shut down.
So, as I said, somebody carrying a gun in this situation without the training may as well be a holding a paperweight for all the good it will do. It is very unlikely they will be stopping any massacres, not unless they've had actual combat training.
It all has to do with brain chemistry. Your brain has three basic parts: the reptile brain, which deals with automatic functions (breathing, heartbeat, etc.), your mammalian brain, which handles instinct and the "fight or flight" response, and the higher brain, which handles thinking and logical thought. Because the higher brain is slower to react, when adrenaline starts pumping in an survival situation, your higher brain shuts down and the mammalian brain wakes up and takes over.
If you've been through military or police training, all their firearms training is exactly about training the mammalian brain in what to do. So, once the higher brain shuts down, the mammalian brain knows how to aim and use a gun, etc. If you haven't been through this training, all the information on how to aim and use a gun is stored in your higher, logical brain...the part that just shut down.
So, as I said, somebody carrying a gun in this situation without the training may as well be a holding a paperweight for all the good it will do. It is very unlikely they will be stopping any massacres, not unless they've had actual combat training.