Police were called to Halls Head College on Tuesday afternoon to confiscate a plastic toy gun brought to school by a student.
About 2:30pm, officers attended the school on Casuarina Drive after being told by school administration that they had the firearm.
Police seized an Air Soft Rifle. The rifle is not capable of being licensed and fires plastic ball pallets.
The weapon was not used to threaten, harm or put students in danger.
It is alleged the student wanted to show friends the rifle.
The 15-year-old student from Falcon is assisting police in the investigation.
Senior-sergeant Steve Thompson from Mandurah police, said the toy, while not a firearm, could have been mistaken for one.
The novelty gun shoots small beads, and was not reported to have been used to threaten anyone.
“People can mistake these for other things,” Snr-sgt Thompson said.
“The message is, don’t bring these things to school.”