Students and teachers in rural Pennsylvania have been armed with buckets of rocks as a last resort to fight back against school shooters.

Every classroom in the Blue Mountain School District, situated 145 kilometres north-west of Philadelphia, has been given a bucket of river stones to defend themselves against armed intruders.

District superintendent David Helsel said throwing rocks at school shooters was more effective than crawling under desks and waiting, and it gave students and teachers a chance to defend themselves.

The buckets are kept in classroom closets.

The plan was implemented late last year, prior to last month's shooting at Marjory Stoneman Douglas High School in Florida, which rekindled the debate in the US about how to protect students from school shootings.

Mr Helsel said the rocks were one small part of the overall security plan for the district, which has about 2,700 students at three elementary schools, a middle school and a high school.

Staff and students in the Blue Mountain district are trained in a program called "ALICE", which stands for alert, lockdown, inform, counter and evacuate.

"We always strive to find new ways to keep our students safe," Mr Helsel said.

The rocks are part of the "counter" portion of training, fighting back if the intruder makes their way into the classroom.

Tactic labelled illogical and irrational

The tactic has been criticised by security expert Kenneth Trump, president of security consulting firm National School Safety and Security Services, who called the idea illogical and irrational and said it could possibly cost lives.

He said arming kids with rocks filled an emotional security need, but did not actually enhance security.

But parents and students have been supportive of the plan.

One high school senior said throwing rocks was better than throwing books or pencils.

Parent Dori Bornstein said: "At this point, we have to get creative, we have to protect our kids first and foremost.

"Throwing rocks, it's an option."

ABC/AP