Teenagers who are permanently excluded from school are twice as likely to commit serious violence within a year of their expulsion than those who were merely suspended, a large-scale new analysis of police and education records has shown.

London’s Violence Reduction Unit (VRU), set up to tackle the number of teenagers dying as a result of knife crime in the capital, said the new research is the first direct evidence of “a clear link between children being excluded from school and involvement in violence”.

It will lend new weight to calls by youth charities, lawyers and other experts for schools to rein in the soaring numbers of ­exclusions.

Government data released in November last year revealed that there were 4,200 permanent ­exclusions in the autumn term 2023-24, an increase of more than a third on the same term the year before.

The study, published in the British Journal of Criminology by researchers at Hull University and Bristol University, followed more than 20,000 young people who were excluded from secondary school, using their education and police records.

They were matched with a second set of 20,000 children chosen because they had the same educational experience, ethnicity and social background, and had been suspended the same number of times but, crucially, were never excluded.

The researchers found that within a year the excluded children were more than twice as likely to commit serious violent crime than their peers who were on the same path towards being thrown out but were not excluded.

In the excluded group there were 990 serious violence offences and 20 murders or “near-misses” in the 12 months following the exclusion compared to 500 serious violence offences and fewer than 10 murders in the group which avoided exclusion.

Lib Peck, the director of the VRU, said: “For the first time, this new research provides ­evidence of what we have long known: there is a clear link between children being excluded from school and involvement in violence.”

She added that what struck her most was that the results didn’t show young people getting involved in violence some years down the line, “but in fact almost immediately after having been excluded”.

Supporters of firm discipline in education argue that with behaviour problems spiralling since the pandemic, exclusion is an essential tool.

Tom Rogers, a history teacher and director of Teachers Talk Radio, said that exclusion was a necessary tool when “extreme behaviour” threatened teachers as well as pupils.

“There is too much focus on ­supporting perpetrators rather than victims here,” he said.

“There are 30 children in each class who could be negatively impacted by the instigator of violence, bullying or abuse. These other children need protection.”

Peck admitted that some exclusions will always be necessary to keep pupils and teachers safe but said more should be done to support these children to stay in school.

Government data shows children on free school meals, black-Caribbean children and those with special ­educational needs and disabilities (Send) are among those significantly more likely to be permanently excluded.

Iain Brennan, professor of criminology at Hull, who co-authored the research, said: “If you are excluded and no longer in well-supervised education, who are you hanging out with during the day? The ­opportunities for being exploited increase, and how you see yourself is also likely to change.”

He added that teachers he spoke to frequently told him that “the writing was on the wall” long before a child was excluded, with external issues including domestic violence and poverty contributing to worsening behaviour at school.

“If a teacher is managing a class of 30 and has limited resources and time, it’s often easier to rely on behaviour policy rather than trying to work out how to include and help that child.”

However, he warned that failing to rein in exclusions risked “letting down the most vulnerable and ­traumatised children” as well as potentially creating victims of crime and “heaping pressure on prisons”.

Kiran Gill, CEO of The Difference, a charity set up to tackle the social injustice of lost learning, called on the government and schools to “sit up and take notice” of this new research.

She warned that pupil referral units, designed to provide alternative education for children who have been excluded from mainstream school, are having to turn away children across the country because they are already full, and many councils are not meeting the legal requirement to find a place in education for children within six days.

“That means these children are at home, or worse, on the streets,” she said.

“Teachers might think that if they permanently exclude a child they will get more support than they can access in mainstream school, but this research shows that is often not the case.”

Gill warned that children were not only more likely to be criminally exploited ­outside school but also to spend much more time on their phone, where they might be influenced by extreme ideologies.

Kate Aubrey-Johnson, a barrister at Garden Court Chambers in London, who co-founded the School Inclusion Project, a group of 200 lawyers offering pro bono support to children facing exclusion, said: “These statistics are shocking but sadly come as no surprise. Any criminal lawyer knows this to be a stark reality for children.”

She added: “The vast majority of children are excluded from school for relatively low-level disruptive behaviour that too often arises from unmet needs relating to Send.”

She said that excluded children typically become isolated and lose self-esteem, making them an easy target for gangs. “They lose hope that they have a future worth living for.”