NOT beating a dead horse, but everything I read says that the police protocol..

[Cosmocat]

5. This is the case in our county

as you noted, it was implemented after Columbine.

At least once a year all of the PD and other law enforcement in our area do drills in our actual school buildings, they try to rotate to different buildings in different districts.

The protocol is that as soon as at least three, ideally four or more, LEO arrive at the school, they create their own tactical team and immediately enter the building to "eliminate" the threat. It could be a borough officer, a township officer, someone from the sheriff's office. Doesn't matter.

Another in a LONG list of reasons that having school staff have guns is a horrible idea. They would get center massed with a dozen bullets once LEO entered the building and saw them.