A rural school district in Pennsylvania is arming teachers and students with buckets of rocks as a last resort should an armed intruder burst in.

Every classroom in the district northwest of Philadelphia has a 19-kilogram bucket of river stones.

Blue Mountain School District Superintendent David Helsel says the rocks are one small part of the district's overall security plan.

He says throwing rocks is more effective than just crawling under desks and waiting, and it gives students and teachers a chance to defend themselves.