At a struggling inner-city secondary, referred to by its teachers as a "hell-hole" and its deputy head as "fucking tough", things are about to get tougher still. Ofsted is visiting and a sense of doom has enveloped the school. But one teacher feels it more than most. He has learnt that he will be taking three of the worst classes in this "challenging" school, one of them twice, on the day that inspectors are expected to tour the classrooms.
It is break-time the morning before the inspection and the teacher is still wincing at the prospect when the deputy head sidles up for a chat.
The senior member of staff then starts to reel off the names of more than a dozen of the most challenging pupils from the "worst" three classes. Initially, it seems like a nasty exercise in vindictive gloating.
But just as the already-anxious teacher is about to explode, his leader places a reassuring hand on his shoulder. He tells him not to worry: "None of these little shits will be in tomorrow, you have my word."
The teacher asks how he can be so sure. Despite - or perhaps because of - their mission to disrupt, these pupils have an excellent attendance record. The deputy head says nothing, reaches into his inside jacket pocket and shows him an inch-thick wad of #163;20 notes.
"I learned later that some of those kids had received up to #163;100 or so not to attend school on that day," the teacher reports. "It seemed he (the deputy) had, in total, paid the equivalent of a whole class to truant for the day."
Find that shocking? Then what about the newly qualified teacher whose mental health was sacrificed so that a London school could pass its Ofsted inspection.
The teacher had been doing well in her induction year, but after a single bad lesson observation suddenly received a letter from the school explaining that it was starting the dismissal process.
It was only after the NQT had had a nervous breakdown that she was told in confidence by the head that the only reason capability proceedings had been started was so that the teacher would not be observed during an impending Ofsted inspection.
Then there is the case of the school artwork, highly praised by Ofsted, that has now been laminated, and is loaned out to neighbouring schools and proudly displayed every time inspectors threaten a visit.
There are the schools where certain teachers are told to go off sick when Ofsted is due, and others where highly experienced professionals suddenly appear; schools where the most disruptive pupils disappear for a trip to Alton Towers during inspections; and those where lessons are rehearsed and learnt by heart by pupils in advance so that they can be performed during an Ofsted visit.
These stories, and many more like them, are not unusual, according to the teachers who tell them. They claim they are symptomatic of an inspection system that is "broken" and full of "cover-ups".
"We are all expected to tell lies to Ofsted inspectors or face the consequences from the senior team," one teacher says. "I think it has become the norm.
"If you get outstanding, they do not come back for five years. You can then relax, enjoy the children and have some fun and stop jumping through Ofsted hoops for a few years. That's why."
Critics argue that this "corruption" is the inevitable "dark side" of a highly competitive and accountable education system that pits schools against each other.
If they are right, it could amount to a scandal every bit as damaging as the corruption recently revealed in that other pillar of school accountability - the exams system.
Chatter about deception
Ofsted reports are vital checks on the performance of schools, relied on and trusted by parents and those running and working in the system. If widespread cheating really is taking place, then exposing it would shatter public confidence in another essential aspect of education.
But how much inspection deception is actually out there? Is it a problem on the rise? If so, what is being done to combat it? The worrying answer to the first two questions is that no one really knows.
Anonymous claims that do not name schools are, by their very nature, almost impossible to substantiate. And if lots of schools really are pulling the wool over Ofsted's eyes, then they are unlikely to publicise the fact.
But the amount of chatter around the subject does suggest that something is going on. All the aforementioned accounts came from a single thread on the online TES forum.
It was started in September by an advanced skills teacher (AST) who said they were expected to guest at another school and pretend to be the acting head of science during an Ofsted inspection. Within a fortnight, more than 80 similar stories or weary sighs of recognition had been posted. And this was only one thread. At least 110 contributions were posted in April under another topic headed "Worst thing your school has done because of an Ofsted visit".
Ofsted told TES that it was "disappointing" to hear of such cases. But while the watchdog did not actually deny that the problem existed, a spokeswoman suggested that in reality such scams would be difficult to carry out successfully.
"Inspectors consider the views of parents, talk to pupils and teachers, and examine documentary evidence to establish if what they observe is typical," she said.
"If schools were excluding large numbers of pupils, this would be picked up when we review attendance records. If a teacher from another school was asked to stand in, we would quickly become aware of their limited knowledge of the school during feedback from their lesson observation.
"We would also expect pupils to comment on anything that was out of the ordinary on the day of inspection, such as rehearsed lessons."
So all is well then? Certainly Jan Webber, inspections consultant for the Association of School and College Leaders, says she has not come across any evidence of sharp practice among schools facing Ofsted.
She too points out that inspectors examine school attendance records when they visit. "If attendance was suddenly down, I am sure Ofsted would follow the trail and find out where these pupils were."
And as far as schools drafting in teachers from outside for inspections is concerned - "How would they do that?" Ms Webber asks. "Inspectors do have lists of school staff, so how would schools explain that certain staff were missing?"
So perhaps the stories above are no more than that - just stories, unverified urban myths passed around by keyboard gossips exploiting their internet anonymity. Maybe the idea of cheating Ofsted is just a fantasy.
If so, it has fooled some very powerful people. In April last year, as Michael Gove launched new behaviour guidance, the education secretary revealed that he thought schools had been hiding their problems from the watchdog.
Teachers had told him that "weak teachers are invited to stay at home, we make sure disruptive pupils don't come in, and the best teachers are on corridor duty", he said. "We put on our best face for inspections."
Which was why, Mr Gove said, he wanted Ofsted to be able to conduct no-notice inspections.
"It is only by having that power that we can be certain we will deal with these entrenched problems," he said, adding: "We rely on Ofsted to let us know how behaviour is in many schools."
Those no-notice "dawn raids" are now taking place, but only on a limited basis. Ofsted has been selecting schools from a pool of about 500 or so that have been judged "satisfactory" overall and have behaviour that is satisfactory or worse.
The launch of the policy in July prompted what sounded like an admission from Ofsted that there had been a problem. "If you know Ofsted is coming - even if it is just 24 hours before - behaviour is one of the things schools can quite quickly do something about," a spokeswoman for the watchdog said.
But the "dawn raids" do not apply to schools without behaviour problems. So what if some of the schools where, in Mr Gove's words, "weak teachers are invited to stay at home" are trying to cover up problems with teaching quality rather than behaviour? As these schools have no explicit difficulties with behaviour, they would be missed by the no-notice detection that Ofsted has belatedly introduced.
When approached for a response for this article, the watchdog said it believed the shorter-notice - no more than two days - inspections it introduced for all schools in 2009 would make it "easier for inspectors to see schools as they really are".
So perhaps Ofsted believes that weak teachers are, unlike behaviour, not something that schools can "quite quickly do something about" if they have 24 hours' notice of an inspection.
The accounts on the TES forum tell a different story. The AST expected to pose as an acting head of science was asked to play the role at the school only the night before the inspection.
Another AST reports that several teachers were "on standby" to go in and pose as permanent teachers for an inspection of a neighbouring partner school "at 45 minutes' notice".
And it is the growing number of partnerships and federations between schools that might be making such last-minute scams easier to arrange. That is the view of Professor Mel Ainscow, who believes the practice has been going on for at least a decade.
The Manchester University academic witnessed the "borrowing" of good teachers for Ofsted inspections when he researched schools serving deprived areas in more than 30 English local authorities.
"We have seen this going on for four or five years and we have seen it in a fair number of places," Professor Ainscow told TES in 2006.
"It is a sort of corruption that has become endemic in the system. People use the phrase 'playing the game'.
"There was an authority, for example, that had a teacher who was absolutely brilliant and who had been holding workshops and acting as a consultant.
"Over a period of weeks we saw him appear on the staff of several schools as they were being inspected by Ofsted."
Professor Ainscow, who went on to head up the last Labour government's Greater Manchester Challenge school improvement scheme, said that local authorities "in quite a few places" had been advising heads to exclude difficult pupils or place them on the special educational needs register to help get their schools through Ofsted inspections.
"It is the dark side of national policy," he said then. "It is not the instinct of schools to do this. But once you know that other people are up to this kind of thing, inevitably you are tempted to join in." Today the academic's "instinct" is that these practices continue because schools are still under the same systemic pressure to compete, a pressure he says goes back to the Conservatives' school reforms of the late 1980s.
It "just forces people to make what are ethical errors", he says, and is intensified by "rumours and gossip" about what is going on in other schools. So even if the stories start out as false, they can quickly become a self-fulfilling prophecy.
Professor Ainscow also recognised five years ago that this "corruption" was being facilitated by the close links senior staff in different schools had forged while taking part in collaborative school-improvement schemes. That collaboration and its associated clusters, federations and chains of schools have only grown in the interim.
The academic is not arguing against such collaboration - far from it. He believes that it is the key to improving schools, by raising expectations and sharing out teaching resources more equitably.
Professor Ainscow wants Ofsted to "rise to the challenge" and inspect groupings of schools at the same time. This would allow greater transparency about the joint arrangements and make it much harder for schools to try to con inspectors.
But his proposal raises another problem for Ofsted. Drawing a line between illicit swapping of staff and genuine collaboration aimed at supporting a struggling school might not always be easy.
In March 2004, Endeavour High School in Hull hit the headlines when angry parents accused it of trying to cheat an inspection. The day Ofsted arrived, nine pupils had begun a week-long vocational course at a local college and four teachers from other schools, including a secondary run by Endeavour's then temporary head, had been drafted in.
"Inspectors won't get a fair view of the school," one parent complained to TES.
But the chair of governors was unrepentant. "This isn't to hoodwink Ofsted - they're aware of what's happening," he said. The chair said teachers from the head's other school had been brought in "to ensure that Year 11 pupils get a better standard of teacher than they would if we got any Tom, Dick or Harry off the supply list".
The head himself made no apologies for trying to get as good an Ofsted report as possible and putting "the best face on things". In the event, Endeavour was placed in special measures, though there was no suggestion that the borrowing of staff was a factor.
But in a case like that, how are inspectors on short visits supposed to know whether staff are being borrowed as part of a legitimate and sustained attempt to raise standards or as part of a cosmetic, temporary fix to get through an inspection?
Blowing the whistle
In 1999, when confronted with a dossier of allegations about schools' attempts to cheat Ofsted, David Willetts, then Conservative shadow education secretary, suggested that heads should be required to sign certificates of authenticity to confirm that the staff they saw were an accurate reflection of the school's resources.
There is no sign of such a rule being introduced now the Tories are in government. But even if it was, would it really do much good? It might make the stakes a little higher for a rogue head. But if they were prepared to try to falsify an Ofsted inspection, why would they baulk at dishonestly signing a certificate?
One might expect that whistle-blowing teachers with a conscience, appalled at what their heads were doing, would be a more effective way of combating the problem.
But read the accounts on the TES forum and you quickly get a sense of why such teachers might be somewhat reluctant to come forward.
The NQT who suffered a nervous breakdown after being put in for capability proceedings so that her school could pass Ofsted writes: "To unjustifiably destroy an individual's career, self-belief and mental health for the sake of being 'a risk' in an Ofsted (inspection) has been the most callous thing I have ever experienced from another human being in my life."
But despite all that, she decided not to expose her school: "I wanted to blow the whistle to bring this to justice, but didn't for the sake of my school's reputation and the other teachers who are under enough pressure without a follow-up visit."
Another contributor, the AST expected to pose as an acting head of science, offers a cautionary tale of what can happen if you do become a whistle-blower.
"I revealed everything to the inspectors and was promptly sent home and threatened with dismissal," he writes. "I never did return. The school (where he was "guesting") went into special measures and I left my school after a big disagreement with the head over acceptable and reasonable behaviour."
Tom Trust publicly warned of schools cheating Ofsted when he appeared before the Commons education select committee in November 2010. The supply teacher told MPs how, on the day inspectors visited a secondary, he was asked to go to lessons that did not need cover and already had teachers.
The reason, he was later told, was that these were "terrible classes", but if Ofsted thought they were being taught by a supply teacher the lessons were less likely to be observed.
"Ofsted's views on behaviour are not worth the paper they are written on, in my humble opinion, because there are lots of strategies that headteachers use to avoid the Ofsted inspectors seeing the worst children," Mr Trust told the committee. "That may shock you, and you may think that that is an isolated incident, but it is not - it happens."
But despite being willing to put his own head above the parapet, today he still refuses to name the school concerned. The reason is that, like the NQT, Mr Trust does not want to put the school in a worse position and let his colleagues down.
A combination of personal fear, loyalty and concern about the damage that exposure could do to a school is preventing teachers from coming forward with detailed accounts of this kind of cheating.
Yet they and the education secretary and academics such as Professor Ainscow are in no doubt that the problem exists.
Even Ofsted itself has now told TES that it is "aware of cases where schools appear to have behaved dishonestly".
"They include", it says, "schools (that) have sent disruptive and challenging pupils on school trips on the day of inspections, schools (that) have sent letters to the parents of disruptive pupils to ask them to keep their children at home to work on projects away from school, and a headteacher manipulating attendance data."
But a spokeswoman also admitted that even though the watchdog logs every complaint, it does "not collect data about schools that might have behaved dishonestly".
In other words, despite the fears of everyone from Michael Gove down, Ofsted is not even attempting to find out just how big this problem is - a problem that has the potential to undermine public confidence in its findings.
After being pressed by TES, the watchdog eventually worked out that there had been 38 complaints about "a school's conduct or activities" during inspections carried out between April and November 2011.
Of course these cases are, by definition, only those where someone with insider knowledge has been prepared to come forward. Critics might argue that until the watchdog does more to uncover how much cheating is really going on, then the credibility of this crucial pillar of the education system remains at serious risk.