It started out as a bit of a play-fight, but they are not playing any more. The older boy has his classmate in a headlock and it is clear that the smaller pupil is not enjoying it. In fact, he has gone ominously quiet.

A teacher has spotted the fight, but visibly hesitates before moving. You can almost see her weighing up the options: intervene and potentially face an allegation of assault, or stand by and risk the pupil getting seriously injured.

But there is no time to debate the issues; fast action is required. Fortunately, Alastair Reid is on hand. He strides up to the fracas and tells the aggressor to let go and move away. But the boy is now “in the zone” and refuses to comply. Mr Reid grips the attacker’s hand and tells the victim to turn his head to the side, leaving his airways unimpeeded. Then, in a quick twisting motion, he pulls the hands apart and releases the strangled boy.

This time there is no permanent damage. The “children” are in fact two teachers taking part in a role-playing exercise at Randal Cremer primary in Hackney, east London.

All 70 members of staff at the school are taking part in the session, to learn restraint techniques in the event of having to separate fighting children.

“We don’t have a lot of problems here, but we can’t be blase,” says headteacher Valerie Serrette-Figaro. “If there’s a fight, we need to know how to contain that while remaining within the law and keeping everyone as safe as possible.”

But the precise level of restraint teachers can use is a matter of debate. At one extreme, schools adopt a “no contact” policy, where teachers never intervene physically. This carries its own risks, however. On top of the potential loss of authority as pupils flaunt their untouchable status, teachers could be accused of neglecting their duty of care by failing to intervene if a pupil is in danger.

In an attempt to clarify the situation, then schools secretary Ed Balls told this year’s annual conference of teaching union, the NASUWT, that teachers should not face retribution if they intervened when children were out of control. “Teachers have the powers and protection to use force,” Mr Balls said.

The 2006 Education and Inspections Act gives teachers the right to use “reasonable force”, but this in itself is problematic. “The Government has still failed to define what ‘reasonable’ looks like,” says Sharon Liburd, a solicitor for the Association of Teachers and Lecturers. “Our members are very concerned about what they should or shouldn’t do.”

Government guidance is that at least one member of staff in a school should have expert training in restraint techniques. At Randal Cremer, the training is being provided by Team Teach, founded by former deputy head George Matthews. His experience in special schools led him to set up what has now become the UK’s largest provider of what he terms “positive handling” techniques, but he says demand for the courses is growing among mainstream schools.

“Special schools are now quite secure in knowing how to manage disruptive behaviour, but all schools must be more on the ball,” he says.

Mr Reid, the trainer running today’s session, recognises that teachers can be reluctant to lay a hand on pupils. He says his aim is to make them feel confident about when they can touch pupils - and how much force they can use.

At one level, this can mean escorting a pupil out of the classroom or away from a situation with an open hand just above one or both elbows. At the more extreme end are situations where a pupil’s safety may be jeopardised.

Mr Reid shows the watching teachers how to help a child who is being throttled: turn their head to the side to shift the pressure away from the airway, and then squeeze the attacker’s arms to release their grip. The same techniques apply if it is the teacher being strangled.

Physical intervention is a last resort, however. Before that, a teacher should attempt to use verbal persuasion. “Be specific,” Mr Reid advises. “Tell them what you want, not what you don’t want. Saying, ‘Stop strangling me’ will probably result in a tightened grip. Instead, say, ‘Let go of me’.”

De-escalation techniques - defusing potentially volatile situations before they turn physical - are the priority. Mr Reid tells the assembled teachers that body language and voice are often key, particularly when children are so agitated they no longer hear the words you are saying.

To demonstrate, he splits the group into pairs, with one acting as a pupil and the other as a teacher. Those playing the teachers are told to quickly approach “the child”, stand close to them and shout. Those acting as the children instinctively flinch and avert their eyes, but an angry pupil would almost certainly lash out, Mr Reid explains. This invasion of the pupil’s intimate space makes them feel uncomfortable and more likely to use violence.

As an illustration of the effect of standing in such close proximity, teachers playing pupils report feeling agitated when they are forced to make eye contact at close range. Some of the “pupils” also resort to nervous laughter. Yet the teachers are not impressed with this “lack of respect”.

In the discussion following the exercise, some teachers admit to telling pupils to “look at me when I’m talking to you”, or to “wipe that smile off your face”, before Mr Reid explains that both responses were entirely natural for anxious pupils.

Even standing within arm’s length places the teacher within “the circle of danger”, Mr Reid says, swinging his arms in an arc to illustrate where a punch could land. Instead, he advises remaining beyond the reach, whenever possible.

He suggests adopting a “calm stance”, standing sideways on or at a reasonable distance, not blocking the pupil’s path and making it easy to back away.

It may seem that new teachers are the most likely to benefit from these techniques, but Mr Reid says the most experienced staff are the most commonly injured. Complacency means they get too close to pupils and put themselves at risk, he says. It is not usually a good idea to wag a finger at an already anxious or angry child: it is just one finger away from a fist and could be bitten clean off by a worked-up pupil.

Another role-play exercise looks at how to deal with a pupil who explodes with rage. A volunteer plays this role convincingly, making a great show of storming out of the classroom, pushing the teacher out of the way and screaming “Leave me alone!”

In the first scenario, Mr Reid chases after her, driving her farther away and prompting more swearing and disruption.

Next time around, he softly tells the angry pupil that he recognises her distress and is ready to listen to her. He uses her name and stands his ground. Although the “pupil” still storms off, her head pops round the corner to check that she is being followed. Eventually, once she has calmed down, she returns.

Implementing these principles has helped to reduce problems at nearby Shacklewell Primary School in Hackney. Staff used to spend about eight hours a week restraining some 30-odd pupils, which included dealing with the aftermath of volatile behaviour, says headteacher David Bridson. Now it devotes no more than half an hour each week, usually due to a handful of “lively” pupils.

It is not a cure-all, admits Mr Bridson, who sports a large purple bruise above his left eye as proof. This came courtesy of a headbutting pupil and acts as a painful reminder of the potential for violence in the classroom.

“You have to be able to read the behaviour as if it were a language,” he says. “I try to look beyond the aggression and work out what the child is really trying to tell me.”

This fits with the message that the first person who needs to control their behaviour in a crisis is the adult. Their body language, tone of voice and choice of words could trigger or diffuse a problem before it even begins.

Ms Serrette-Figaro says that a lot of the training is simply putting a name to what her staff already do. But it is crucial to keep abreast of changes and best practice, she adds.

While it is much better to prevent situations from turning violent, Mr Reid says that there will be times when teachers need to physically intervene.

“Failure to take reasonable steps to protect children from harm could open individuals to charges of negligence,” he says. “People need to be clear about why it is necessary to use force and then use it with confidence if need be. Usually, it is to avoid a greater danger.”

By anticipating what could go wrong, teachers are fulfilling their legal obligations. “It comes down to power and choice,” Mr Matthews adds. “Staff have the power to use force, but it is ultimately their choice. They also have a duty of care to safeguard children, but that is not a choice.”

Just as teachers are taught what to do in the event of a fire, so they need to know how to act in the face of extremely challenging behaviour.

Team Teach courses cost #163;90 per person. For more information, visit: www.team-teach.co.uk

WHEN TO USE REASONABLE FORCE

When a pupil is:

- committing a criminal offence

- causing injury to themselves or others

- damaging property

- prejudicing good order and discipline.

Source: The use of force to control or restrain pupils: Guidance for schools in England (April 2010), DCSF: www.teachernet.gov.ukdocbankindex.cfm?id=14800

THE ABC OF RESTRAINT

Act

- Stop and think.

- Adopt a calm, non-threatening stance and posture.

- Slow your voice and give clear verbal directions.

- Pause and allow time for delayed compliance and help to arrive.

Balance

- The likely outcomes if force is used against the likely outcomes if force is not used.

- The best interests of the child against the best interests of other children and the rights of staff.

Choose

- Who should intervene, where and when.

- The minimum of force necessary to achieve desired result.

Source: Team Teach, Dynamic Risk Assessment Checklist.