The only thing that stops a bad guy with a gun is a good guy with a gun.
Implied in the NRA claim is the notion that the United States is a nation as lawless and hopeless as Pakistan; so much so that teachers are being trained with firearms in order to prevent further massacres. The NRA implies that the US government is so inept and so corrupt that it is incumbent upon schools and private citizens to protect children from madmen. The NRA argument is that the United States is a third world country, like Pakistan, where lawlessness rules.
Given that the above video is the embodiment of what the NRA is advocating, it is unequivocal that the NRA is the hopelessly outdated organization that is impeding progress in the United States.