Gun laws stop school shootings? Where in the US does that work?

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?

What kind of state or federal law do you propose, with the unlikelihood that the 2A won’t be repealed?

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.

That’s not how amendments work

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.

The thing is gun laws won't protect against school shootings unless you basically completely disarm the population--which is not realistically possible as there would be too much non-compliance. And note two things about the data:

1) Many sources seek to inflate the number of school shootings by counting incidents in which the school is only incidental, not the target. Think drug deal in the parking lot when school is out etc. And note that counting firearm deaths to minors counts mostly gang vs gang stuff.

2) It is almost certain that guns save more people in self defense situations than they take in all mass shootings (using the realistic test of public and indiscriminate targets--again, the numbers are inflated by things like gang fights), let alone just school shootings. (And, no, I do not believe Lott's numbers. He's way high and an awful lot of what he does count is deterred robbers and the like, where death was unlikely in the first place.)