The shocking picture of illegal weapon-carrying - often for protection by bully-victims - was uncovered as part of ongoing evidence of a major review into national behaviour and attendance (NBAR).
Professor Ken Reid, who heads the review team, stunned headteachers with his emerging picture of fear, intimidation and violence among the school-aged population at the annual conference of the Association of School and College Leaders Cymru in Llandrindod Wells last week.
But he also said there is no evidence that guns - fast becoming the trademark of many teenage gangs in some English inner cities - are carried by pupils in Wales.
Instead, he claimed they are more likely to stash small knives or even keep "sticks" on them to deter bullies on their school journey.
Speaking at the conference, Professor Reid, deputy principal of Swansea Institute of Higher Education, said young weapon-carriers often did not feel safe without them.
But a final NBAR review, ordered by former education minister Jane Davidson in March 2006, is not expected to be published until next spring, with recommendations on tackling bad behaviour and poor attendance.
In an interim report released this September, Professor Reid said schools were generally managing bad behaviour well, something he repeated at the conference.
But he hit out at the rise of "Big Brother" behaviour by some pupils, particularly girls, as a result of the controversial Channel 4 TV programme in which bad behaviour often led to fame and fortune.
"The problem is, we have gangs, third-generation truancy and the Big Brother culture to contend with," he said.
He also claimed heads often felt compromised over behavioural issues.
Professor Reid called for better government guidance on pupil restraint. He also said governors should have more training and wants more funding for the plans.
Brian Lightman, ASCL'S national president, said Professor Reid's comments were "disturbing".
A government spokesperson said the review could lead to new Wales-only legislation. "Implementing the changes is likely to imean taking forward an Assembly Measure," he said.
Leader, page 28.