Let’s forget for a moment that arming teachers is a bugfuck stupid idea. If you actually tried to do that, this is what you buy:

Insurance Liability.
Range time approaching that of a police currency requirement.
Shoot/don’t shoot legal training.
Weapons and training ammunition.
Salary increases to overcome teacher/staff resistance.
Additional teachers to cover training lost time.
Teachers’ union reaction.
Parental lawsuits, before and after the first shooting.