A Pennsylvania school district has a different solution for tackling intruders: rocks.
Buckets full of river stones have been placed in all classrooms at the Blue Mountain School District in Schuylkill County, Superintendent David Helsel said.
If students at the rural school district can't evacuate during a shooting, they don't have to sit and wait.
"Protocol has been that students lie down, under desks and basically become passive targets on our classrooms," Helsel said. "We decided to empower our students with tools of self-defense if needed."
In a video posted online, the superintendent said the district decided to bring rocks to the classrooms after staff members took the active shooter response training, ALICE -- alert, lockdown, inform, counter and evacuate.
The training taught them how to barricade doors with desks and chairs, and run away from gunfire. It also encouraged students to throw everything, from pencils to staplers, at potential shooters "rather than wait passively" for them "to attack."
"At one time I just had the idea of river stone. They're the right size for hands, you can throw them very hard and they will create or cause pain, which can distract," Helsel told CNN affiliate WNEP.
But they only see it as a last resort.
"We've learned many things from these tragedies over the years," Helsel said. "One of them is that evacuating makes students the safest."
And if students can't leave the building, they'll have their stones.
"We understand that a gun is much more deadly than a stone. It's our hope that we can somehow stop the ability of an armed intruder to enter our classrooms," he added.
Parents appear to like the district's plan.
"At this point, we have to get creative, we have to protect our kids first and foremost, throwing rocks, it's an option," parent Dori Bornstein told the affiliate.
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