Well, now we should give guns to the first graders to protect themselves from stupid teachers?
If we have widespread concealed carry of guns by teachers and school administrators there will inevitably be cases where students get their hands on a gun and either accidently or intentionally shoot other students. The kids are smart enough to figure out who is carrying a gun. Also, accidental gun discharges are more common than people think so having a bunch of loaded gun carrying teachers/administrators walking in crowded school hallways is a recipe for disaster.