Every room would have to have a door that can be secured with sufficient locks or crossbars to make it secure. Glass in doors would need to be, altered or removed or the door replaced so access could be made through the glass.

The entrances to the school should also be made secure so the glass in the doors could not be broken out, or shot out, that would allow unauthorized access. A camera at each entrance would assist in identifying the person wanting access.

I believe the expense for upgrading the schools with secure doors in every room and adding a hard wired alert system would be an expense parents and citizens could support and would be an expense significantly less than having police or armed guards, metal detecters etc added to every school.