[scarmig]

"School shooting" is a polysemous phrase. There's the very literal version--a shooting that happens at a school--but also a more specific one that refers to a much rarer situation--a lone kid consciously plans to go in and shoot a lot of people en masse, as a kind of suicide that is intended to leave a permanent presence on a community that the kid viewed as having wronged them in some way. The former is much more relevant for policy making, but in public discourse the latter plays the disproportionate, defining role. OP is frustrated by that vacillation. School shooter drills are almost irrelevant for the modal literal school shooting, but they inflict psychological damage on students and even create the archetype of the statistically rarer type in the public imagination.