Why not just create an app? Everyone’s got a phone. Write an app and have teachers register with the system. A few taps on the phone and the cops know where to go and what’s happening.
1) Start app
2) Choose situation
3) Choose room number
4) Send
Cops have layout of school and have preplanned potential access/observation points.
Easy peasy.
That only works if you actually have cops wanting to make entry, instead of milling around outside.