Allow some teachers who have a concealed carry permit to carry if they want to.
What you are not considering is that primarily, the administration does not want teachers to be carrying guns and that at least 80% of the faculty and parents do not want teachers to be carrying guns. You cannot force this on the students, faculty and parents of a school. As well, teachers who do not like guns will quit. There will be a flood of teachers leaving schools that allow guns to schools that don't, and the schools that allow guns will have a hell of a time recruiting more teachers. Most people do not want teachers to be carrying guns. It is a RW gunnut thing, not what most of the country wants.