Last year schools were given the power to search pupils for knives
Almost one in five teenage pupils surveyed for a police study said they had carried a weapon in the past year.
The survey of 1,426 14 and 15-year-olds by Portsmouth University researchers suggested only 5% took these to school.
Some 60% of those who carried a weapon said they did so for self-defence, while 30% said they had done so during activities with the Scouts or cadets.
Only 20 of the youngsters surveyed admitted carrying a weapon for the purposes of an attack.
The study was carried out among pupils in Southampton last November and was commissioned by Hampshire Police after the fatal stabbing of two young people in the city.
The report of its findings, Staying Safe and Out of Trouble, suggested only a very small proportion, some 3.9%, were part of a youth gang that sometimes did things against the law.
They were almost exclusively male.
It also found that the vast majority of the young people, 71%, felt safer in school than outside.
Report author Professor Carol Hayden said it showed a lower rate of weapons carrying and gang membership than some national surveys.
It sent a reassuring message about the majority of young people, she said, but did raise concerns about a minority.
"Although most of the problems to do with these issues are outside schools, there is a small problem in schools."
Chief Inspector Andrew Bottomley said the research had been commissioned so his force could do something meaningful to try to stop youngsters carrying knives.
He said: "The data that we now have means that we can work closer with schools and youth services to tackle this problem head-on.
"We now have a true reflection of young people's attitudes and feelings, not just about carrying weapons, but also about whether they feel safe and how big a problem bullying is for them.
"It's important to understand all of this so that we know why young people feel that they have to carry a weapon for protection.
"Knife crime is a growing trend nationally. It's a community problem which needs long-term solutions."
In May last year schools were given the power to search pupils suspected of carrying weapons.
Under the guidelines, searches should be carried out by trained staff, authorised by the head teacher and should only take place where there no risk to staff or pupils.