[JonathanDnk]

And another point - how may of those school shootings ended before anyone the student called could do anything whatsoever to impact the situation? You are using 1 in 2500 based on counting all school shootings, but some 98% of those are over in seconds or at most a couple minutes.

From what I can tell, there's only been ~10 school shootings in history that involved "active shooter wandering the halls from class to class shooting large numbers of children." One every couple years in modern times. Far more often, either the shooter only had one target from the beginning, or only stays in one classroom, or is stopped right away. Extreme events like Sandy Hook, Parkland, and Columbine are burned into our collective memories, but only about half-a-dozen other incidents fit that mold in K-12 schools.