Luke Walmsley was stabbed to death at his school in Lincolnshire
School staff will need body armour when new powers to search pupils for weapons come into force, a teaching union says.
From next Thursday head teachers will be able to authorise staff or security guards to carry out such searches.
The Professional Association of Teachers says staff who carry out searches must be trained and should have access to protective clothing.
But the National Association of Head Teachers says where there is a clear risk teachers should call the police.
General Secretary Mick Brookes from Nottinghamshire said his union was advising teachers not to tackle pupils they believed to be concealing a weapon such as a knife.
"Where there's a clear danger our advice to members is to call the police who are equipped and trained to do just this sort of thing."
Solicitor David Brierley from Derby-based union the PAT said the Department for Education and Skills guidelines, due to be published on Thursday, set out useful advice for difficult situations.
But he warned: "Rather than just conducting a weapons search, the process should be risk-assessed.
"In relation to searching for knives in schools we would like protective clothing to be considered as part of the risk assessment."
Knife incidents rare
He added that staff could not be forced to carry out such searches, and one option was to hire security guards.
But if a member of staff was prepared to carry out a weapons search then it was the school's responsibility to make sure they were not exposed to unnecessary risks, he added.
Mr Brookes said he was not in favour of schools taking funds out of their budgets to employ security guards to do the job police were already paid to do.
Metal detectors were only likely to be appropriate in a very small number of cases.
It was up to head teachers and school governing bodies to decide if they thought such scanners were necessary.
He added: "You've got to ask yourself where on earth are we going as a society if that's what we are having to do?"
Knife incidents are rare but several high profile cases, including the stabbing to death of Luke Walmsley in Lincolnshire in 2003, have prompted the government to bring in the new powers.
Education Secretary Alan Johnson said incidents involving knives were rare, but one crime caused by a violent weapon was one too many.
"I want schools to take a zero tolerance approach to knives.
"That's why I have given head teachers these tough new powers to search for weapons."
He added: "Schools can also now use metal detector arches and wands to screen pupils for knives where the head feels this is right.
"I think parents will welcome the clear message we are sending that bringing a knife into school will not be tolerated."