Reassuring presence of police on patrol
But most local authorities have found it difficult to get police officers to carry out the role.
A report on the Safer Schools Partnership scheme in July found that most local education authorities had not filled all their posts in schools identified to have a police officer. The project aimed to have 100 officers in schools.
Lancashire police were exempted from the scheme because the relationship they had with the schools was already good.
Sir Charles Pollard, the acting chairman of the Youth Justice Board, interviewed last week after the tragic death of a 14-year-old schoolboy at a Lincolnshire school, said he wanted to see an extra 100 officers stationed in schools.
But an initial evaluation of the partnership scheme said that a dedicated officer was expensive and that forces were likely to pull them out of schools if they were needed for more urgent duties such as terrorist threats or murder investigations.
The report, by a joint inspectorate including the Office for Standards in Education, found the presence of police officers led to good early identification of young people who were at risk of committing crime. There was also some evidence of a reduction of crime in the immediate community - although not all authorities had monitored this.
It recommended that local authorities and local criminal justice boards should monitor the impact of a school police officer on the number of exclusions, the incidence of bullying and truancy.
A spokeswoman at the Department for Education and Skills said: "Clearly, any initiative that is proving successful in improving security in our schools has potential for expansion."
The Youth Justice Board, which co-ordinates reforms of the youth justice system, said 100 police officers for schools had now been found.
* A 15-year-old boy has appeared before Skegness magistrates court charged with murdering a 14-year-old schoolboy at a Lincolnshire school last week.