Problem i see is the majority of teachers are liberal and won’t even touch a gun.
To my surprise I have not found the aversion of guns to be a problem with teachers. Most of them would prefer to carry whatever their politics.
The trustworthy ones can qualify for a CCW without any problems. The others aren’t going to be able to qualify.
It might be helpful too to state in your recruitment ads that you must be willing to get your CCW. Build the marketing.