I wonder if the only way a law like that could work, would be to let the teachers whom already own handguns, choose if they feel comfortable wearing a concealed (or exsposed) weapon during school hours.
There are millions of gun owners in the US. Many of them also have a license to carry (both concealed and not).
It stands to reason that some of them are teachers.
That could potentially work. However, I think we need to be focusing on the people they have already hired to be on school grounds who have the proper training. Rather than arming teachers, we should be checking out the security guards to make sure that they're not going to blunder around when something happens, like they did in Florida.