If a particular number of teachers were allowed to conceal carry in a school, they could easily stop a threat. Just think of this: why don't they have certain teachers undergo extensive mental stability tests, firearm safety courses and keep a coded firearm safe in classrooms out of the reach children? Also it would be a good idea to require an annual review of mental stability for these teachers to carry weapons.
Gun control laws will not end gun related crimes. Think of this: cocaine is illegal, but countless people across the US still buy, sell, and use the drug. The same thing would happen with a gun ban. A criminal is going to have a gun regardless of what the law is, because he's a criminal.