An 11-year-old boy spent three hours in a police cell after he brandished a plastic toy gun at a schoolmate and told him to "hand over the money".
Earl thought he would end up going to prison after his arrest
Earl Crump, from Sheerness, Kent was arrested and taken to Sittingbourne police station after the incident at Cheyne Middle School.
His mother, Tracey Crump, said she thought the punishment was too harsh.
Kent Police said it acted in the public interest and any reports of firearms were taken extremely seriously.
Officers were at the school dealing with another matter when Earl was caught with his toy gun.
"Two officers arrested a boy at school on suspicion of possessing an imitation firearm in a public place," said a police statement.
"The boy's mother was present when he was taken into custody."
At the police station Earl was searched and had a DNA sample and fingerprints taken.
After three hours in the cell he was released without charge.
A toy gun like the one Earl used to threaten his schoolmate
"I thought that I would go to prison and I wouldn't see my mum or my brother again," he said.
"It was too severe a punishment for an 11-year-old boy just playing in the playground," said Ms Crump.
Headteacher Peter Woollacott said school policy did not allow weapons or imitation weapons to be taken beyond the school gates.
"We take it very seriously if children bring in weapons or imitation weapons because of the nature of the world at the moment," he said.
"In this case Earl made it far worse because he used the weapon to threaten another child."
The school said it was not its decision to have Earl arrested but his mother said he was so upset he did not want to go back.
Her son said he had no intention of taking any gun into school again.