Assuming any staff members or faculty carrying firearms would be untrained is, not to put too fine a point on it, asinine.
A better question would be, who many teachers, janitors, administrators, etc., etc., already have a CC permit, or are military veterans?
We have trained, armed guards at airports, on planes, in banks, courthouses and government buildings, why not public schools?
The NRA (among other organizations) offers certified firearms training. If a teacher wants to carry a sidearm, they can take such a course. I had to get an IT certification as a condition of continued employment, cost me $300 bucks out of my pocket. If I can do it, they can too.