Ideally, this would not be an issue. However, if a hypothetical attacker is presenting guns and other weapons that are possible to be used at a distance, it only makes sense to have the defenders using distance weapons. Tasers might also be useful, but what if the attacker has a finger on the trigger? The last thing you would want to do is send a jolt of electricity through him.
School safety is more dependent on keeping the staff aware of the situation and well coordinated. Giving teachers or staff members guns would probably do more harm than good, especially in cases of misfire or those who are not well equipped for handling a gun. It is better to keep the guns for the professionals.
Arming teachers and school staff is the not way to ensure the safety of students and staff. Arming people is a reactionary response, not a preventative response. School violence and facility security needs to be addressed by preventive planning, the implementation of security and emergency protocols.
In the vast majority of US schools there is no screening of visitors and no limitation on access to the building. Addressing these issues is the way to improve school safety.
There is a number of ways to keep a place safe, and a gun is not needed to do so. While guns do have their place, I do not believe a school is one of them. If kids get caught in the crossfire more tragedy will happen then good. Tasers, or a well knowledged security officer can keep our schools safe.