Amy Klinger, co-founder of the Ohio-based Educator's School Safety Network, said that rather than arming them, schools should train teams of educators to assess threats. The calls by Trump and others for guns in schools have "really taken the focus off things that are more effective," she said. "We need to do things that work, not that feel good."

Klinger said more guns on campus can lead to more accidental shootings, including two earlier this month in Minnesota and Florida, and it's unreasonable to expect even armed staff on large campuses to be able to stop a mass shooter.

"We need to train our teachers how to identify these people. People don't want to hear that — they want a quick fix," she said.