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.
"Rather than just conducting a weapons search, the process should be risk-assessed. We would like protective clothing to be considered as part of the risk assessment."
