My idea will not curb all gun violence, but it may prevent shooting deaths in schools. The idea is to have every classroom door locked all the time -- not just when a teacher gets a warning or hears shots, but ALL the time when class is in session.
Attach a key to the hall pass for kids who need to use the restrooms. If the principal wants to drop by, he has an intercom to inform the teacher. And when he or anyone else gets to the door, they knock. And nobody gets in without a "Who is it?" from the teacher -- which will also be a good lesson for kids opening the door at home.
Wouldn't this be a lot simpler and more effective solution than arming teachers or having armed guards in the schools?