More than a thousand children were caught with weapons in school last year, according to a survey of 29 police forces in England and Wales.
The weapons included knives, blades, knuckledusters and a Taser stun gun, the Press Association survey found.
The children included a 14-year-old with a sword and a four-year-old with an unnamed weapon.
Head teachers’ leader Geoff Barton said the findings were “grim but unsurprising”.
The survey, which follows concern about rising levels of knife crime, was based on Freedom of Information data from police forces.
It found schoolchildren involved in incidents with many different types of bladed weapon, including lock knives, penknives, craft knives and garden shears.
In Bedfordshire, a pupil was caught in possession of a machete and in Manchester a samurai sword was recovered from school premises.
Thames Valley police discovered a bayonet in a school and in the West Midlands, a 15-year-old was found in possession of an axe.
The figures showed 1,072 incidents involving weapons, up from 831 in the same areas in the previous year – but did not include statistics from the biggest force, the Metropolitan Police in London.
The data was based on the financial year – and the survey found another 311 incidents between April and August 2019.
“Serious violence is a growing problem amongst young people and we continue to work closely with partners to address this,” said Chief Constable Olivia Pinkney, lead for young people on the National Police Chiefs’ Council.
“Police involvement in schools, whether it be officers delivering talks and interactive sessions or based in schools themselves as part of the Safer Schools Partnership, helps us to educate young people and explain why carrying a weapon is never the right choice.”
But Lucy Martindale, a youth worker from south London who campaigns against knife violence, said: “The situation is getting worse, even just this year.
“Some young people I speak to say before they leave the house – where most people check they have picked up their keys and wallet or purse – they check they have their knives with them.”
Mr Barton, general secretary of the ASCL head teachers’ union, said this is a problem that schools cannot tackle on their own and called for more community support and “investment in policing”.
“The scourge of weapons has grown worse in recent years, and while there are a number of complex factors involved, a key issue has been cuts in policing and local support services for vulnerable families.
“Gangs have filled this vacuum and often pressure and groom young people into dealing drugs and carrying weapons,” Mr Barton said.
A Department for Education spokesman said £10m had been invested in “behaviour hubs” to share information between schools on improving discipline.
“We have strengthened teachers’ powers so they can take action if they suspect a pupil has brought a prohibited item, including knives, into school.”