Why do you think that banning guns is the only solution to stopping school shootings? Better school security and allowing teachers to arm themselves May be just as effective.
It's not the only solution, but I feel it's the best(of many that need doing) solution at this time.
The cons of armed teachers, in my opinion, outweigh the Pros.
Pro - Teachers can shoot other shooters on sight.
Pro - Lower cost than hiring someone to protect the school.
Pro - Teachers feel safer.
Cons - Teachers become a primary target both for active shooters AND for law enforcement. (As said law enforcement may not know if a teacher is the active shooter)
Cons - Teachers may try to go at it alone and leave their students alone.
Cons - There's a gun in the classroom or hallway that could be stolen at any given time.