A school gun ban does not protect professors, teachers and students. It protects only politically correct administrators, newspapers and governments from possible lawsuits.
As the law stood, a mentally deranged person with a grudge and no regard for the law could attack defenseless people at schools and churches. If they believed a janitor or principal were armed, they would probably forgo an attack.
In early New England, settlers were required to carry their firearms with them, even to church.
How times have changed.