Students start turning up at school wearing matching purple shoelaces. Graffiti tags begin to appear on walls around the site. Unsavoury characters on BMXs start lurking around the school gates when the bell goes.
Rumours abound that the school has a "gang problem". But just how much do schools need to worry about gangs? Are they really penetrating the nation's schools? Are graffiti tags and playground brawls symptoms of an alarming problem or just part and parcel of school life?
And if a school does identify a problem - within its own walls or affecting pupils in the local community - what can it do? Are metal detectors and embedded policemen the right approach, or is it better to get children involved in thought- provoking drama workshops? Is it enough to stagger school closing times to protect children from the postcode wars on their way home? More crucially, what can the school do to prevent youngsters falling into gang membership in the first place?
Quantifying the problem
Researchers have tried to quantify the problem of gang culture in schools, but few have found convincing evidence that it is widespread. Ofsted's Managing Challenging Behaviour report from 2005 found gang culture was "perceived to be a problem in one in five secondary schools" in England, but "few schools had evidence of it".
One in five of the 11,000 teenagers in the Safer London Youth Survey carried out in 2005 said they would call the group of friends they hang around with "a gang" but less than 4 per cent were in a gang that had a name and a designated territory.
And academics who have studied gang culture at close quarters say much of the panic over perceived increases in gang culture in schools is overblown. Many gangs, they say, are friendship groups far removed from the organised criminal fraternities at the heart of the drugs trade.
Simon Hallsworth, gang expert and professor of social research at London Metropolitan University, says youth gangs have become "a folk devil par excellence", being blamed for everything from last August's riots to school failure and dangerous dogs.
"Group violence is not a new problem in schools - it is part of our perennial history. There's always going to be a bunch of hard kids there saying, `You're gonna get your head kicked in,'" he says.
The current trend is to look to schools to solve many of the problems teachers know are bound up in a complex web of social issues they cannot tackle by themselves.
The final report of the Riots Communities and Victims Panel, which investigated the possible causes of the 2011 riots, called on schools to play a key role in preventing youth violence.
Published in March, After the Riots says schools are failing to improve the "resilience" of their charges sufficiently, and suggests they "should assume responsibility for helping children build character" and introduce a "character test" in order to "help them realise their potential and to prevent them making poor decisions". How welcome such an initiative would be on the ground is uncertain.
The report also highlights the fact that many parents believe schools are not doing enough to tackle truancy - a key factor in youngsters becoming involved in gang activity. But schools are already inspected on attendance, and many will feel that there is not a great deal more they can do with the resources they have available.
So, amid all the headlines, the rhetoric and the blame, what can every school realistically do to broach the issue of group violence inside and outside school, whether it has already identified a risk or not?
Graham Robb, a former head who now serves on the Youth Justice Board and leads the advisory group on education on the Westminster government's new Ending Gang and Youth Violence team, which emerged from a report on the subject last year, outlines a simple list of things every school can consider.
"First, you need to send a very strong message to all pupils that most children aren't in gangs, aren't carrying guns and aren't committing crime. It is important to establish positive social norms," he says.
Schools should also be wary of the offers they get from training and drama organisations to carry out anti-gang work. A whole industry has sprung up with consultants offering quick-fix interventions - often imported from the US - that may not have proved their worth. "Schools need to ask what the evidence base is for the work," Mr Robb says.
He stresses that "shock tactics", such as schemes to take young people on tours of prisons, in the hope that it scares them off crime, have been shown to be ineffective.
"Pupils need to engage with moral dilemmas, questions of values," he says, adding that all programmes need very careful preparation and follow-up work.
School staff should also make themselves familiar with any court orders their pupils are subject to and the conditions of those orders. "Schools play a huge role in preventing reoffending," he says.
Forming links with local community, ethnic and faith groups is also essential for building the trust of parents, he adds.
Striking a balance
Once these things have been considered, a school has to decide what balance to strike between preventative, educational and enforcement approaches.
Clearly, a school with no identified gang problem is not going to install a metal detection archway, but it may wish to invite a drama troupe to provoke discussion among its students about responsible decision- making.
A 2009 report by the NASUWT teaching union, Gangs and Schools, highlights that enforcement techniques such as weapons searches can be used effectively. But it warns that schools need "to consider carefully their response to avoid placing those who carry weapons through fear at greater risk of exclusion and therefore involvement in gangs".
Professor Hallsworth of London Metropolitan University has written about securitised school sites turning children into a "potentially criminal population" before any crime has been committed. Other leading researchers have also warned against excessive use of enforcement-led approaches.
In Merseyside - an area where gang problems hit the headlines in 2007 with the accidental shooting of 11-year-old Rhys Jones in Croxteth - police believe that they have helped schools to strike a balance.
The force has 34 schools officers stationed full- or part-time in 60 secondary schools under the Safer School Partnerships programme, which it has been running for the past eight years.
"Embedded" officers carry out a variety of tasks, from tracking down truants to delivering PSE lessons on citizenship, responsibility and safety. They use everything from DVDs to restorative justice sessions to deliver key messages to students. But officers will also deal with flashpoints and incidents on site.
Merseyside Police has also been pro- active in its use of drama to reach pupils at schools in at-risk areas. In 2008, it commissioned a play, Terriers, and a supporting 10-week educational resource mapped against the key stage 3 (S1-3) English curriculum, showing the consequences of becoming involved in gang culture.
Pupils are encouraged to explore moral dilemmas through creative writing, storyboards and monologues. Another version has been developed for use in primary schools, as the imperative to target children early increases.
The Metropolitan Police has shown a strong interest in the project, bringing it to five gang-affected schools in London in March. But there may be even simpler methods to reach students at risk of falling into gang culture and crime. Experts on the front line say many young people simply need to be listened to and have a key "parent figure" or mentor to nudge them on to the right track.
The power of drama
Many of the experts we spoke to agree that drama and role play can be vital in helping youngsters to think and talk about their feelings in relation to gangs and street violence.
And while the NASUWT union warns that schools should be wary of the quality of the organisations that offer programmes, there are good ones available.
The publicity for Bare Drama, a play exploring gang culture and prevention produced by Birmingham's Women and Theatre, says: "Young people can be sensitive to hectoring on `issues' and are often resistant to work on subjects that are sensitive or exposing.
"Theatre provides a forum for them to explore complex situations."
Women and Theatre's projects coordinator Pippa Frith adds: "You can have discussions about issues very close to home through the creation of fictional characters. Pupils can project their own emotions onto characters without admitting they are having those feelings. It opens a dialogue and gives them a voice."
But she also sees theatre's limitations: "Drama is never going to do everything on its own- there needs to be a lot of activities around training and education as well."