As tens of thousands of Americans march for tighter gun control laws, a Pennsylvania school district has turned to arming students with rocks as a “last line of defence” against mass shootings.

The Blue Mountain School District in Schuylkill County has equipped 200 of its classrooms with buckets of river rocks in the event of a mass shooting.

District superintendent David Helsel revealed the novel plan in a committee hearing on school safety on 15 March following last month’s shooting at a Florida high school where 17 people were killed.

“Every classroom has been equipped with a five-gallon bucket full of river stone,” Mr Helsel told the hearing.

“If an armed intruder attempts to gain entrance into any of our classrooms, they will face a classroom full of students armed with rocks and they will be stoned.

“We have some people who have some pretty good arms. They can chuck some rocks pretty fast.”

Mr Helsel explained the river stones were his idea and were placed in classrooms two years ago having initially considered using golf balls.

“We chose to make it well known about the river stone because if it’s an existing student [they will] be aware that the chances are they’re going to be stoned severely if they try to do anything,” he added.

“We didn’t want our students to be helpless victims,” he later told Reuters. “River stones were my idea. I thought they would be more effective than throwing books or book bags or staplers.”

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