There was an armed school resource officer at Columbine. He exchanged shots with one of the shooters there. The armed officer at Marjory Stoneman Douglas infamously hid for the duration of the incident.
Armed security is theater at best.
Armed security is theater at best.
The latter really scares me as a teacher. Imagine what the security guy could do with some planning time and full access to all locked doors as well as the camera and alarm systems.
Never mind stealing, armed guards sometimes just forget and leave their weapons in the bathroom. A list: <https://giffords.org/lawcenter/report/every-incident-of-mish...>