The US has never tried this. For an example of efficacy we have to look at other wealthy western nations that have strict gun laws and see how many school shootings they have. The data overwhelmingly indicates this works.
As a counter-point, where in the US has any law stopped teenagers looking at naughty things on the internet?
Don't look at school shootings, they don't matter. What matters is how many, not by what means. Note that the most deadly such attack was with a truck, not a gun.
The data proves nothing about whether it works because it's a cultural problem far more than it is a means problem. They choose to go out in a blaze of infamy rather than be a nobody. They generally are planned long in advance, there's plenty of lethal things they can get their hands on.
Easy, just do the same thing as other western countries. If the 2A is an obstacle, then change it. The unlikelihood of and changing the 2A is the heart of the problem, not an constraint to be worked around. The question is why are gun rights sacrosanct, but other rights can taken away just by saying 'think of the children'.
If you think the 2nd Amendment is bad now, just wait to you see what happens if we're unlucky enough to ever have a Constitutional Convention in our lifetime.
As a counter-point, where in the US has any law stopped teenagers looking at naughty things on the internet?