The Gilmore College student showed the inoperable handgun to a teacher and police seized the replica weapon.
The school issued a letter the next day to parents of the student�s class, notifying them of the incident and assuring them the student had not threatened anyone.
An image of the letter was posted on social media and the school then sent the letter to the rest of the school body.
An Education Department spokeswoman said the circumstances were very similar to a recent incident at Comet Bay Primary School, where a student brought a handgun to school to show his friends.
Kwinana police station officer-in-charge Senior Sergeant Steve Thompson said no charges had been laid but police had talked to the boy, who had been curious about the object.
�If anyone finds a handgun, replica or not, leave it in the position it was found and contact police,� he said.