I have been thinking about the idea of having an armed and trained person stationed at every school and I've seen something mentioned on another forum that doesn't sound too outlandish.
What about using a rotating schedule for member of the Armed Forces aka National Guard for legal reasons. They are already on the Government payroll and making this a part of their duties isn't beyond the realms of possibility.
I don't think that military uniform/garb would work in schools as it could scare children and adults alike but perhaps there could be a more civilian looking uniform adopted? Also I don't think that the idea of an automatic weapon being carried around in plain view is all that great so I'd limit it to sidearms or other concealable or non-blatant firearms.
It's just a thought and certainly not fully baked.