[null and void]

The 911 operator who KNOWS there is a drill may quite reasonably dismiss a civilian call at a nearby address as just someone who saw the drill and in their excitement named the wrong school.

It might take several calls from different people for the realization that there really is an active shooter at the other school to soak in.

Say 3 calls, a minute each? That's about the average duration of an active shooter event. It's a long time if you're being shot at! It's also very fast for a response once the call get to the local LEOs

[Valpal1]

All true, which is why choosing a scheduled drill day for a mass shooting at another location would be attractive to a shooter. It’s also a finger in the eye to perceived authority and society which would also increase its value the theses socially maladjusted killers.