Teachers with guns, hmm...
Are they human? Yes. Do they have rights that must exist through logic and reason? Yes. Is one of those rights the right to their own life? Yes. Logically, if one has the right to life must they also have the right to defend it? Yes. Does that right still exist at the workplace? Yes. It stands to reason, then, that teachers in the workplace must be allowed the means with which to defend their own lives.
But there's another level to this: Are those teachers both logically and contractually placed in a guardianship over children who are not legally, and often mentally incapable, of understanding and protecting their own rights to life? Yes. The responsibility to protect those lives falls on the guardian, the teacher, and to be able to exercise that responsibility a teacher must be allowed the means to exercise it.
The whole guns-in-the-workplace argument brings up another dilemma, and that is people carrying guns on others' property. Before you enter another person's property (house, Walmart, workplace) you must first respect their right to their property. They might not want you to carry your gun on their property - their rules are their rules. But here's the catch: Can the manager of that Walmart, or the principle of that school, absolutely guarantee the protection of your life at all times, as if you yourself were in charge of protecting it? No, they can't do that. And that's why this dilemma has been brought up in court already, and many businesses are now allowing guns on the property, the premises being that customers feel their ability to defend their lives is being restricted. Now, they could simply shop somewhere else, yes, but in the interest of keeping customers happy many businesses have allowed their customers to carry concealed weapons.
My workplace allows guns. Most if not all places like it will, simply based on the demographic of people in the machine business. They do it because it just makes sense - what if some crazy ass walks through the unlocked doors during the workday and starts shooting at workers who can't defend themselves? That's not a problem where I work. It shouldn't be a problem where anybody works, anywhere, ever.