State certified annual training course.
Curriculum could be time on SOP, basic marksmanship, draw and fire, move and fire, cover and concealment, etc. not unlike gunsite, thunderranch, blackwater, etc.
Volunteering teachers can seek out all the additional instruction they want, perhaps with some training schools offering accredited courses that go toward the training requirement. I would imagine that a teacher could get a discount rate for training. Need I say the words?
Longarms are pretty much out within the classroom environment for many reasons, such as theft, unauthorized use, etc.
Flexible and rapid response is best achieved with a concealed sidearm by teacher and staff on the school grounds.
Operational security is best achieved with a concealed sidearm.
No one knows who is armed and who is not (hopefully). This is the key.
Teachers could have a sit down together to drive this point home.
Consciencous objectors advised to keep their traps shut. As in, it is your duty as a public school teacher, if you will not carry, to at least maintain operational security and keep silent on the issue.
Might be a fun vacation for some teachers to buddy up and head off to Gunsite academy or the likes.
As far as legal .. does the state think parents of murdered kids are not going to seek damages for failing to implement defenses?
State requires children are educated.
State provides for schools.
State is responsible for child safety while going to, at, and going from school.
So, if the state does not want to be open to liability, they must implement a viable and realistic means of immediate defense.
The best means, IMO, is concealed carry.