Chief constables offer heads advice on pupils thought to be carrying weapons, report Jon Slater and Graeme Paton.
The police are to advise headteachers on how to deal with knife-carrying pupils.
The Association of Chief Police Officers said the advice would be similar to that on how to handle drug-related incidents.
Last week, new powers to allow heads to search pupils suspected of carrying knives without having to involve the police were included in a package to tackle violent incidents in schools.
The moves follow the death of Luke Walmsley, 14, who was fatally stabbed in a Lincolnshire school corridor last year. Last week an 11-year-old boy was stabbed in the leg by another pupil on a school bus. The youngster was attacked as he was being driven home from Fitzharrys school in Abingdon, Oxfordshire. Two 11-year-olds were arrested.
Charles Clarke, the Education Secretary, who unveiled the clamp-down on classroom violence, said school staff should not have to wait for police to search pupils.
Tony Melville, ACPO spokesman on knife crime and assistant chief constable of Devon and Cornwall constabulary, said: "While we welcome the opportunity to work in partnership with our colleagues in the education service to combat the carrying of knives in schools, there is a need to consider seriously issues such as staff safety and training."
Heads say they would be reluctant to put staff in a position where they might be endangered by a knife-wielding youth.
David Hart, general secretary of the National Association of Head Teachers, said: "Giving heads the power to search for offensive weapons is an option, but it puts their safety very much at risk. The real answer is better liaison between police forces and schools."
Clarissa Williams, the head of Tolworth girls' school, Surrey, said: "The real concern we have is that when we call the police it is left to the whim of a telephone operator whether or not they prioritise the call.
"We have had incidents recently when people have come on to the school grounds but when we ask police for assistance they fail to arrive straight away. If these reforms on safety are going to work we need the back-up of the police."
A fairer sharing of hard-to-place pupils and limits on the number of excluded pupils admitted by individual schools were also included in a package of support for schools, designed to improve behaviour.
But grammar schools will be exempt from the local agreements after the Government said reports that they would be forced to take pupils who have not passed the 11-plus were wide of the mark.
Key measures include:
* schools will be expected to sign a "statement of expectations" on pupil behaviour, including zero tolerance of bullying and verbal and physical abuse of staff.
* a consultation paper on improving investigations into pupil allegations against teachers; and
* agreements to allow heads to request unannounced police searches for knives.
The Government has also promised that in the new year it will publish proposals to tackle the compensation culture which is deterring teachers from taking pupils on school trips.
Chris Keates, general secretary of the National Association of Schoolmasters Union of Women Teachers, said: "I have real concerns about the appropriateness, efficacy or desirability of the suggestion that schools should be able to conduct searches themselves."