More than 1,000 children were caught carrying knives in schools last year - with the youngest aged just four, new figures show.
A total of 1,144 knife possession offences in schools, where the suspect was a child, were recorded in England, Scotland and Wales in 2018.
Dyfed-Powys Police were called to one school in Wales by teachers concerned that a four-year-old had a knife.
And in Manchester, an 11-year-old, who had replaced a highlighter nib with a blade, told another pupil: "Listen to me or else I'll stab you."
Former teacher, David Simmons, said he was once confronted by a six-year-old brandishing a knife while working in a north London school.
"He was threatening other staff members and saying that he was going to stab them so I've gone over trying to calm this child down," he said. "He's then said he's going to stab me and kill me."
Weapons seized from youngsters by police last year included machetes, hunting knives and a samurai sword.
The number of offences more than doubled over the past five years, among the 36 forces in England and Wales that provided comparable data, soaring from 372 in 2014 to 968 last year.
Commenting on the figures, a government spokesman said they had "strengthened teachers' powers" to combat knife crime.
"They can take action if they suspect a pupil has brought a prohibited item, including knives, into schools. These powers include searching pupils or their possessions if they suspect they have a weapon.
"Our Serious Violence Strategy focuses on steering young people away from knife crime and we are also investing over £220 million in early intervention projects."