Teachers are calling for random security checks at school entrances to assess the scale of weapon-carrying among pupils.
By Gary Eason
BBC News Online education editor, in Llandudno
They want a national system of recording violent incidents in schools, many of which they say are not being reported.
The government says it will consider the idea.
One of the main problems may be that children are not carrying weapons with a view to attacking teachers, but to protect themselves from bullies.
But delegates at the NASUWT teachers' conference, in Llandudno, also spoke of violent children using knives, iron bars and ball-bearing guns in schools.
Teachers want airport-style security checks
The union's deputy general secretary, Chris Keates, said the health and safety reports that schools are supposed to file could underpin a national database of violent incidents.
She said a problem was that it seemed many schools were not completing these as they should - even though that was a breach of their legal duty.
The union did not want to create the impression that the problem was rife in schools.
"Alternatively, if we have got the tip of an iceberg with children arming themselves perhaps against cases of bullying, it's essential everybody knows what the true picture is."
Ms Keates said: "We have asked for a sample run of airport-style security checks in schools to identify the level of offensive weapon carrying."
She acknowledged that - as with random drug tests - parental consent could be an issue.
"We believe the vast majority of parents support this because they see it as a safety issue. It's as much in the interests of parents for the safety of their children."
The conference debate on the issue focused on violence against teachers.
Joy Windsor, from Hampshire, said union surveys had suggested a teacher somewhere was being abused one way or another every seven minutes.
But there was no nationally agreed system of recording incidents.
It was important that whatever was introduced did not imply the teacher who was a victim of an assault was unable to cope with the job.
Nor must there be "quasi performance tables" compiled by government or the media showing which schools had the greater problems.
A member of the union's executive, Brian Garvey, recalled how one of its members was shot in the back in a school corridor.
"The head's response? 'Well, it was only a ball-bearing gun - we have excluded the boy for three days'.
"That boy should have been on a charge, never mind three days' exclusion," he said.
"But the school didn't want the police in, did they? It wouldn't do them any good in the publicity stakes."
But, he argued, it would show the school was prepared to stand up and look after people.
Another executive member, Ron Clooney, said Southampton was to be congratulated for having agreed, finally, to ask every school in its area to report every incident so it was out in the open and they could deal with it.
Sian Luscombe, a behaviour support service worker from Newport, made fun of the phrase, "emotional and behavioural difficulties" or EBD.
"Those challenging individuals who turn up Every Bleeding Day," she said.
She wanted to run a parenting course in "naming your child".
"In my long referral list there are very few Elizabeths, very few Timothys, several Kyles, lots of Charlenes - and Kylie, spelt in many ways."
But Ron Clooney said later that although poor parenting might often lie behind children's behaviour, it was not a class issue.
"This is a mythology that's grown up that social deprivation breeds indiscipline. It's not true.
"I have had children from nice homes carrying knives.
Home-made weapons recovered from schools in the Southampton area
"It's not just inner-city deprived schools it's happening all over the place - for want of a better definition, good middle-class environments.
"Is it that they may be latch-key children - are they being emotionally abused by parents who are using TV as a babysitter?
"The children watch violent films. The parents are never there. There's no input."
A teacher who works with pupils who have been expelled from schools said teachers should treat children as they wanted them to be - not as they were.
Simon Whitney, from Suffolk, said: "With so many difficult pupils you must use your knowledge rather than your instinct.
"Treat children as you want them to be, not as they are. If you do this they will live up to your wishes."
A spokesperson for the Department for Education and Skills said: "We have great respect for the work of NASUWT and its members and ministers will give careful consideration to their suggestion, although decisions on individual schools' security arrangements are normally for heads - working with their LEA and local police - to determine, as they know their schools best".