A generation ago, the idea of having a police officer based at a school and working alongside staff would have seemed anathema to most teachers.
Not any more. Since the Safer Schools Partnership (SSP) was set up in 2002, the presence of uniformed officers has become increasingly common, and more and more popular with politicians.
Indeed, Schools Secretary Ed Balls seems to believe this initiative could solve many of the problems perceived to be rampant among England's pupil population - including gang culture, violent extremism and the use of weapons.
But the widespread adoption of this scheme begs a host of questions: whether the presence of officers undermines teachers' professional autonomy; whether they unnecessarily criminalise children; and whether the partnerships indicate the pervasiveness of a police state.
These questions gained greater urgency when it emerged last week that even more schools were signed up to the SSP than previously thought. There are now 5,000 schools with police on tap - 10 times more than previous estimates.
The Government had been cagey about the total number, saying the various types of partnership made it impossible to know how popular the scheme was. But a new survey by the Association of Chief Police Officers shows that 20 per cent of primaries and 45 per cent of secondaries have a partnership or other formal arrangements with the police.
New government guidance suggests SSP officers are dealing with relatively minor issues, leaving experts puzzled about why Mr Balls and Jacqui Smith, the Home Secretary, want the system to expand.
A typical case was when an SSP officer was called into an Oxfordshire secondary to deal with a Year 8 boy who had slashed another child's blazer with the blade from a pencil sharpener. The pupil did not report the incident, but his mother did, using the constable's contact numbers - which were posted around the school - rather than speaking to a teacher.
The officer told the assailant's mother that he could arrest the boy, and the child admitted the offence only when told that he could be taken to a police station. Fortunately for him, the victim's mother agreed to a "restorative conference" between the two boys.
Because of the increasing number of children entering the criminal justice system for seemingly minor offences, about a year ago police were given new, softer powers to hand out on-the-spot warnings or arrange meetings between victims and offenders.
Restorative justice is now increasingly being used in schools and communities to resolve problems. So far, SSP officers have tackled bullying, violent extremism, drug and alcohol abuse, weapons and gang culture. They have also worked with others to help victims of domestic violence and sexual exploitation. In addition, they can assist during managed moves - whereby pupils at risk of exclusion are given a fresh start at another school - and teach children about financial fraud through citizenship lessons.
SSPs were initially offered only to secondaries with behaviour or crime problems; now ministers want every school to form a partnership. But to do this, heads will have to persuade their communities that this does not mean there is evidence of serious problems among their pupils.
Efforts to form more partnerships might also be hampered by a general election: the Conservatives believe putting police in schools shows that children are out of control.
Ms Smith and Mr Balls say officers in schools are there to provide a "guiding" hand for teachers. But shadow schools minister Nick Gibb argues that the partnerships waste valuable police time.
According to Martin Bayliss, head of Holyhead School, in the deprived Handsworth area of Birmingham, there is every chance that partnerships will not work unless schools are allowed to choose the right kind of police officer for the job.
Relationships between police and staff at Holyhead were poor because, Mr Bayliss says, officers repeatedly tried to enter the school site without permission. He says the offer of a partnership was an "olive branch" from a local superintendent who let the head choose an officer. The school picked Alison Geddes, who had run youth clubs in the school and was known for her work with the community.
Four years on, the scheme is working successfully, Mr Bayliss says, because Ms Geddes defers to teachers. "It's not a bolt-on - she is part of our pastoral team and is far happier to leave it to teachers to resolve issues themselves," he said.
"I would argue we respond to incidents in a much more severe way than Alison does - for example, by using exclusions. But for SSPs to work, the relationship between the police and headteacher has to be absolutely top draw. If not, it creates conflict and distrust."
Ms Geddes sits in staff meetings and in the staffroom, but is also called away on other police duties. Her boss, Inspector Helen Kirkman, says it is important that she is not seen as a member of the teaching staff.
"Alison is at the school as a presence," Inspector Kirkman said. "She takes some lessons and assemblies - for example, about the impact of gangs or violent extremism. Schools can look out for sympathy with this - for example, through scrawls on exercise books. She also runs diversionary activities for those at risk of being excluded. Her job is not about arresting people but providing support for them, and she is viewed with the utmost respect by children."
Partnership officers were also called to help at a school in Hounslow, west London, after teachers noticed children were posting "extremist comments" on the internet. They helped teachers to run "prevent" activities, including an assembly, and this has become an ongoing programme.
But if police are not called on to do their usual job in schools, why are they there? Surely a social worker or specially trained teacher could do the same work, argues Will McMahon, director of the Crime and Society Foundation.
"We will get a tendency in some areas where teachers start to defer to the criminal justice system to resolve issues which previously they would have dealt with themselves," he said. "This criminalises the school environment. There are many ways of (carrying out) behaviour management, and having the police in school just means teachers lose their authority at a time when they should be gaining it. Involving children in improving a school is a much more powerful way to create change."
The way partnerships work varies across the country. A PC or community support officer can be based full time in one school, or work across a cluster of schools that are part of a behaviour and attendance partnership. But the headteacher retains responsibility for school discipline. Yet, paradoxically, SSP officers, who still work for the police, are supposed to make their own decisions about when to intervene.
PC Iain McLellan is based at two of the biggest schools in Wythenshawe, Manchester - Newall Green and St Paul's. Both have health workers, mentors, attendance officers, welfare officers, social workers and Connexions advisers on site.
Every Friday night, PC McLellan joins a multi-agency team, including representatives from social services, housing, youth intervention, youth work, youth offending teams and schools. It patrols the local area looking for children who need help or who are in trouble. It also helps children who are misusing alcohol or drugs or getting into fights, as well as those who may simply need advice and support.
"It's a very different culture - it's a great way of working as it allows us to really get to know the young people and make decisions based on what is best for them," PC McLellan said.
The number of these partnerships may grow, but it is far from clear to what extent they will benefit teachers, schools and the pupils they aim to protect.
PARTNERSHIPS IN ACTION
In Camden, north London, the local SSP officers organised an anti-knife football tournament for secondary schools. Officers acted as referees, wearing T-shirts with the slogan "Value your life, don't carry a knife". A reduction in aggressive behaviour among young people in the borough has been reported since the SSP was set up.
At Bridgemary Community Sports College in Gosport, Hampshire, the SSP led to changes on the school site, suggested by a crime prevention officer. A door used by truants and smokers to leave the building was replaced by an electronic door which opens only in emergencies. CCTV cameras were set up. These showed most "incidents" involved new students, so teachers have reviewed their induction arrangements. Truancy "sweeps" at the school have led to a reduction in the number of persistent absentees.
At Abbey Manor College in the London borough of Lewisham, SSP officers check the college attendance roll to see whether any students are engaged with the local Youth Offending Team.