Jon Slater charts the alarming proliferation of such cases and asks: has the pendulum swung too far in favour of pupils' rights?
Mark Harris's nightmare is coming to an end. Last week police dropped their investigation after finding no evidence to support the allegations against him. After a month out of school, his headteacher wants him to return to work as soon as possible.
His relief is obvious - 14 pupil witnesses corroborated his story - but there is no mistaking the bitterness he feels towards his accuser. "His statement was obviously just concocted," he says. "He tried to get his friends to back him up, but they weren't even there."
The National Union of Teachers says the number of calls to its professional and legal services from teachers facing investigation has doubled in the past few years, and since last September the number of members involved in police interviews has been running at around one a day. The union deals with 200 cases a year where a full investigation involving the police or child protection services is launched into allegations that a teacher has abused a pupil.
In 80 per cent of cases, the accused teacher is automatically suspended, a figure which the union says is far too high. Typically, the conditions imposed on Mark Harris are applied so the accused is isolated. But where police are called in, fewer than one in 10 cases leads to a conviction. "The significant majority of teachers leave court with their reputations intact," says NUT general secretary Doug McAvoy.
But even when they are vindicated or have not had to suffer the trauma of a court appearance, teachers may find re-entering the classroom difficult. Those who return often find themselves unsure of their ground when dealing with bad behaviour and wary of being alone with a single child.
Mark Harris is now waiting to find out whether the boy whose allegations threatened his livelihood will be excluded permanently, as the headteacher of his school has recommended to the governors.
Accused teachers bear the brunt of false or malicious accusations, but the rest of the school also suffers. Other pupils experience disruption if their teacher is suspended, especially if the incident occurs in the run-up to exams.
"Too often action taken by governing bodies and local authorities ignores the impact on school life," says Doug McAvoy.
Heads and governors spend huge amounts of time gathering evidence. Pupils and staff know something is wrong but are barred from talking to those concerned. An atmosphere of suspicion and secrecy can develop.
A key decision, and one that has a huge impact on the accused, is whether the person should be suspended pending an investigation.
Adrian Wells was cleared of physically assaulting a 12-year-old pupil at Ysgol Penglais, a secondary school in Aberystwyth - but only after he had been told that the accusation could lead to his own children being placed on the social services' "at-risk" register.
Mr Wells, head of maths, went public last year at the Association of Teachers and Lecturers conference. "Even after I knew nothing more was going to happen, it was still affecting me," he says. "There were times when I walked past incidents I could have intervened in. There were days when I struggled to force myself in to do the job I love. That really hurt."
Colin Brooks, a maths teacher from Redditch, Worcestershire, also faced the ordeal of false accusation. He was suspended for 12 months after an ex-pupil accused him of sexually abusing her. He was arrested in May 1997 after the girl, who had left the school in 1994, accused him of fondling her in the school computer room and in his car while she was still a pupil.
In May 1998 he was finally acquitted of indecent assault by Worcester crown court after the prosecuion failed to produce any evidence. The charges were brought despite a social services report which showed that the girl had psychiatric problems and had made similar claims against her father. Her former social worker described her as "attention-seeking, controlling and manipulative".
Adrian Wells believes that in some ways he was lucky. Having carried out an investigation, his headteacher resisted pressure from social services to suspend him while police investigated the pupil's claims. He credits his headteacher's knowledge of education law and strength of character, and has sympathy for those whose heads are less strong-willed. "You feel isolated enough even when you're at school. Colleagues know something is wrong, but they can't ask and you can't tell them."
Christine Gale, chair of the National Governors' Council, saw for herself the damage that can be caused when a pupil at her school made a false allegation against a teacher. She says: "A teacher who stays in the school needs extra support, and deserves it."
So why, given the devastating consequences, are so many teachers suspended as a matter of course? According to government guidelines (see box), suspension should not be automatic. Indeed, Circular 1095 states that such action may not be best for the school and can be damaging to the teacher. Yet the NUT estimates that in up to 80 per cent of cases, schools take the safe option and suspend, with headteachers and governors often unaware of the guidance.
Doug McAvoy wrote to the Education Secretary, David Blunkett, in November to complain about the number of "over-hasty and ill-judged decisions to suspend teachers". A meeting was promised but never happened.
According to John Dunford, general secretary of the Secondary Heads Association, outside influences often force the decision to suspend. "Heads are under pressure from child protection and social services to act quickly when they would prefer to look more deeply into allegations first," he says.
And "there isn't a governor in the country who wouldn't uphold a teacher being suspended while an investigation is being carried out", says Christine Gale.
But while the education world wrings its hands about the number of innocent teachers suspended, child protection agencies see things differently. "Social services fear that schools have a natural inclination to side with the teacher," says Rob Hutchinson, director of social services in Portsmouth and a member of the Association of Directors of Social Services' children and family committee.
"If the police say there is a possible criminal charge, the headteacher would be unwise not to suspend. (In other cases) you have to balance the interest and safety of the child against those of the teacher. The problem is the length of time the investigations take."
Deciding whether or not to send a teacher home is a problem facing an increasing number of schools. A TES poll last month found that one in 10 teachers had been assaulted by a pupil in the past year and that one in four had been threatened. Mark's story suggests that rather than face up to punishment, pupils are seeking to turn the tables on their teachers.
It is an issue that concerns Michelle Elliott, director of the children's charity Kidscape, who was a governor at a school where a teacher was wrongly accused. "I have divided loyalties. We don't want to destroy good teachers, but if a child makes an allegation which is true and the community turns on the child, that is devastating."
For some teachers, the stigma of being investigated, combined with a long suspension and loss of confidence means they never return to the classroom. Given the recruitment crisis, perhaps that is another reason for heads and governors to think twice before rushing into a suspension.