When there is a school shooting, you should count everyone in the school as deeply affected. Maybe the district.

From wikipedia it looks like there's 13,000 school districts in the US - so 1 in 10 (!!!!) has had a school shooting in the last 22 years. Am I doing this right?

You are assuming that each school shooting is in a separate district in the calculation. That is not necessarily the case, especially with some large school district serving many more students than a small rural district.

But I agree with you that it affects the school and community deeply, even in surrounding communities. I live in Texas, and the whole state was deeply affected after Uvalde. A relative's school got evacuated a few weeks later out of what happened to be a false alarm, with the relative forced to exit the school hands above their head to show they didn't have a gun. They were on the complete other side of the state, probably like a 6 hour drive away.

I'd say far worse. So much US discourse is about school shootings, that it's clear it's affecting people far outside the school districts themselves.

It's affectional national politics.