The U.S government as well as the various state governments do not have the finances to be able to hire and place Police Officers or armed Security Guards in every school so this could be a cost effective solution.
This program would be similar to the Federal Flight Deck Officer program that allows airline pilots to carry firearms on board airplanes to prevent another September 11th but in this situation it would be to help prevent or minimize school shootings.
Such a proposal would ultimately be up to each state to decide whether or not they would exempt there teachers and staff and allow them to carry on school property but such a proposed grant by the federal government could help encourage states to take such action knowing there would be funds to help train there staff members.