Do not be a hero, staff told
Department for Education and Skills guidelines suggest that only in "exceptional circumstances", should teachers take action against a child before police arrive.
It does not identify what such "exceptional circumstances" might be but suggests that two or more teachers should be present and that the child should be diverted away from other children.
However, David Hart, general secretary of the National Association of Head Teachers said: "Clearly it is nonsense to suggest that teachers should be apprehending children with weapons.
"These guidelines are positively dangerous and need to be re-drawn with advice from senior police officers. There are always going to be those teachers who act selflessly to try to protect others but these things are always best left to the police, and this is what needs to be made clear."
Under the Offensive Weapons Act 1996, it is illegal to carry an offensive weapon on or around school premises without good reason.
A "good reason" might be carrying a knife for use in the kitchen, for example. The Act gives the police powers to enter schools, without permission, to deal with incidents.
DfES guidelines urge that, wherever possible, weapons should be confiscated and handed over to police, although staff are under no obligation to attempt to search anyone. They should not attempt to disarm a child if he or she is being unco-operative.
A spokesman for the Association of Chief Police Officers, said: "The message to staff working in schools is no different from what we would give to any other member of the public.
"We would not urge people to take it upon themselves to try to disarm anyone and place themselves, and possibly others, at physical risk, although there will always be have-a-go-heroes.
"Our advice is, withdraw from the situation, draw it to the attention of the school management and, if necessary, call the police."
Traditionally schools regarded matters of safety, such as fighting and bullying, as problems they tackled internally, using their own sanctions and procedures in dealing with the culprits.
However, following several high-profile breaches of security such as the Dunblane primary massacre in 1996, they are now far more likely to call in the police rather than risk harm to staff and pupils.