For less than 5% of the cost of the program you outlined, and with about 300% more effectiveness, the job can be done well in time for fall opening if done as follows.
Allow every teacher and school employee who passes a background check, and desires, to carry a conceal weapon.
I am all for this, but most teachers will refuse to carry. This also will not stop these animals (sorry MSM) from getting into the building and starting a shooting to begin with. Twenty teachers responding to his shooting spree might end up with him dead, but he'll have ample opportunity to take out a lot of victims until that happens.
If students need to pass through metal detectors and have their bags x-rayed, these weapons won't make it into the school in the first place.
Armed teachers are a backup, not the solution.