Ten times more schools than originally thought have police working on site, figures show.
A survey by the Association of Chief Police Officers shows that 20 per cent of primaries and 45 per cent of secondaries in England are involved in Safer School Partnerships (SSPs) or other formal arrangements with the police.
Ed Balls, the Schools Secretary, and Jacqui Smith, the Home Secretary, this week updated government guidance for schools. Partnerships of this type, they say, can prevent pupils becoming radicalised.
In Hounslow, west London, teachers called in partnership officers after pupils left "extremist" comments on a website. Police then ran an assembly on "how to handle risk and live a safer life".
In another incident, officers were called in when a pupil slashed another's blazer with a pencil sharpener.
Mr Balls writes: "We recognise that some schools may be wary that the local community might see a regular police presence on the premises as evidence of serious problems in the school.
"However, an SSP should be seen as a positive commitment by the school to prevent problems arising and it would be a missed opportunity, both for the school and its pupils, if an SSP were not explored.
"SSPs deliver positive benefits for everyone - police, schools, pupils and the wider community - in every area, and that's why we want to encourage every school to consider getting on board."
Graham Robb, a member of the Youth Justice Board, said: "SSPs have been a success because headteachers and police commanders saw that pupils, staff and parents are reassured by the visible sign of agencies working together to keep pupils safe and to prevent crime."