In March last year David Cripps, the headteacher of Radburn primary school in Letchworth, Hertfordshire, checked the post, saw the future and felt a deep wave of nausea swell up inside him. "We get a lot of mail from Ofsted," he says. "But if you get one with a contract number on the envelope then that can only mean one thing - you're going to be inspected. When I saw it I just felt sick. I knew that it was going to take a year out of my life. I knew that there was going to be this colossal amount of work to do and that we would have to put on this big show. I just knew it was going to be horrendous. And it was."

The letter gave six months' notice of the inspectors' visit. No sooner had it arrived than three teachers and one school assistant announced their departure, insisting that they would not go through another Ofsted inspection - the school had been tested in 1996.

Cripps holds up two ring-bound folders full of policies reviewed and revised specifically for the report. In the month running up to the inspectors' arrival, he and his deputy worked from 8am until 8pm every day including weekends. The entire mood of the school changed. "There was just this quiet, manic hysteria," says one teacher.

It seems like an extreme emotional reaction to what is ultimately a 36-page report on the performance of your school. But not, says the chair of the school governors, when you consider the stakes. "If you failed then a lot of staff would probably leave or the head could be fired," says Terry Ware.

Last week all 12 teachers at a primary school in south west London resigned following an Ofsted inspection. Moor Lane junior school in Chessington was found to have "serious weaknesses" by inspectors last April. After a follow-up inspection last month they told the headmistress and chair of governors that "insufficient progress" had been made. The chairman of the governors said the school had been "wrecked" by Ofsted's decision.

In January, a teacher in Eynesbury, Cambridgeshire, committed suicide after Ofsted inspectors criticised her teaching. Pamela Relf, 57, jumped into a river, leaving a handwritten note which made it clear that she could no longer cope with the stress of modern teaching. The school had been found to have "serious weaknesses". Last month Ofsted partly upheld a complaint brought by the school, admitting that there had been a breakdown in communication between its inspection team and members of the staff.

There are basically three things that can happen as a result of a report from the Office for Standards in Education. Inspectors can pass a school, fail it, or decide that it has "serious weaknesses". If a school fails it then goes on to "special measures". The headteacher has to provide an action plan which is sent to the secretary of state for education. Around six months later, inspectors will return to find out whether the school is following its action plan and they will continue to return on a termly basis. The school is expected to be able to turn itself around and get off special measures within two years.

A school with "serious weaknesses" goes through a similar but less extreme procedure and is expected to address its problems within a year.

At Radburn primary, the inspectors finally arrived on a Monday from a hotel they were staying in nearby. It was three weeks into a new school year and Cripps had three new teachers, some of whom were newly qualified. "By this stage," says Cripps, "I felt completely detached." After a short talk the inspectors roamed around the classrooms during lessons. "You just hope that one of the children isn't going to start playing up or come up with something inappropriate," says one teacher. At the end of the day the inspectors told Cripps they had seen one or two problems in the lessons they had seen. He left school late feeling depressed.

On Tuesday they observed more classes and delivered far more positive feedback. "At this stage I went from thinking this is going to be disastrous to this is going to be OK," he says. But when an inspector walked into one class, one of the teachers tried to defuse the tension by making a joke: "I think you must have the wrong room," he said. It fell horribly flat. "No I haven't," replied the inspector. "I can visit any class in the school."

On Wednesday Cripps had a couple of interviews with the inspectors. They asked him about long-term financial planning and he tried to explain that it was not possible to plan long term when you are not in control of your income and funding changes from year to year. "I might as well have been speaking a different language," he says.

That night they told him the school was not a failing school. But that only convinced him they would decide it had serious weaknesses. "Thursday was dreadful. They were supposed to tell us their verdict the next day but I looked so awful that they asked if I would like to know that evening. I said yes and so they went away and then pulled it together and told us the result. He talked about the strengths and then the weaknesses and I was waiting for him to say 'serious weaknesses'. After a while I just stopped him and said, 'Sorry, do you mean serious weaknesses?', and he said, 'No, sorry I should have made that clear. There are no serious weaknesses.'

"Afterwards I felt relieved but mostly I just felt crushed and exhausted."

During the last inspection cycle around 3% of primary schools failed, and around 10% were found to have "serious weaknesses". The reality of working in a failed school, however, is far less clinical than the statistics. "It just creates a mood where everyone thinks it is all right to blame the school for everything," says one teacher who used to work in a failed school. The pressure not to fail comes not just from the school but from the local education authority. If there is a large number of failed schools in one area the government could remove the provision of education from its tasks and take it over itself or hand it over to a private company. By the time these strains have trickled down to ordinary teachers the stress can just be all too much.

Ofsted says it has now reduced the warning it gives schools to six weeks so staff have less time to worry. Schools that get good reports and have consistently high scores in the Standard Attainment Tasks (Sats) will now get less rigorous, shorter inspections. "We have always recognised that inspection is a stressful business," says a spokesman. "Inspectors don't expect to be liked. Partly because it is human nature not to like someone who is there to pass judgment on your work and, more significantly, because teachers have never had to do anything like this before. It is a shock to their collective system."

Teachers have had a lot of shocks to the system in recent years - Sats, literacy and numeracy hours, the national curriculum - and Ofsted inspections will soon be followed by performance-related pay. Those who have been in the profession more than a decade talk as though they are being drowned under relentless tidal waves of initiatives. Yet Ofsted was more than just one more broadside in the battle to overhaul the education system.

Created in 1992, it was born out of the wave of consumer rights initiatives - from the Citizen's Charter to the cone hotline - which can be identified, for better or for worse, as Majorism. "Before Ofsted came along nobody knew what was going on in our schools," says the Ofsted spokesman. "There was no way of the customer, the parents and the children, knowing how good an education children were getting.

"Sensible schools would see it as a free consultancy. It isn't about criticism but about identifying what a school does well and what it does badly."

Cripps does not see it that way. He describes most of the inspectors who came to his school as "pleasant" and "humane" people doing a terrible job. One of them, however, told his deputy: "This is an elite team." When a teacher pointed to the concrete statues the children made in the front of the school as part of a project, the inspector said: "I've seen better."

Ofsted, points out one former inspector, is there to judge, not to advise. "It is essentially punitive. I think if it were supportive it would make a big difference but that is not its function. At the end of the day a lot of it comes down to whether you have a good team of inspectors or not and that hardly seems fair."

So Radburn primary school didn't fail. There was never really any question that it would fail. This small school in Britain's first garden city, which sits on a working-class estate created from the overspill from north London, does not have any of the advantages of schools in middle-class areas. But nor is it located in an area of major deprivation. Of its 226 full-time pupils, 30 have English as an additional language, 60 are entitled to free school meals and 56 are registered as having special educational needs. As such, demands on its teachers are tougher than for some but less extreme than for many. And given the circumstances, it manages well. The Sats at seven and 11 suggest that its average intake arrives well below the national average at seven and leaves only marginally below the national average at 11, indicating considerable improvement.

In this parallel universe where semantics are everything, the Ofsted report claimed there were "significant weaknesses" but not "serious weaknesses" at the primary. Among the findings was real praise. ("Teachers manage behaviour well in lessons." "Pupils are well-behaved and their attitudes to work are good.")

But there were also criticisms. The school had not done enough to improve on problems raised during the last inspection, it was claimed. "The strategic management, financial planning and performance monitory" were "unsatisfactory"; "effective strategies for staff appraisal and the identification of professional development needs," had not been implemented; and "attainment in English and mathematics is generally below average and significantly below average in writing across the school". Inspectors recommended taking 10 minutes off the lunch hour and adding five to the end of the school day to create more time for the basics. The teachers went into post-Ofsted depression - that flat, numb feeling that comes with a sudden release of pressure. Three governors resigned. "They were volunteers and the report was demanding more than many of them were prepared to give," says Ware, the chair of governors.

"From their [the inspectors'] point of view the whole thing is completely data-driven," says Cripps. "It's one way of looking at the world but it's not one that I would subscribe to. I consider my work child-driven. There is a lot of this work that you simply cannot quantify in a report but which is essential to the job." Other teachers said there were some useful things to come out of the report, but none believed that the pain justified the gain.

Sitting outside Cripps' office is "the biter" - a small boy who bit a small girl because she kept saying she was his girlfriend. Soon afterwards comes another small boy who has been accused of pulling a different girl's hair in the playground. He starts off insisting that he didn't touch her. Then he concedes that he might have flicked her.

"It was just a joke," he tells Cripps.

"A joke for you or a joke for her, because it doesn't look like she found it funny," says Cripps, and points him to the floor on the other side of his office door. And so it goes on. The ebb and flow of little people and their misdemeanours, staff requests, paperwork and phone calls. The variety and scale of work that Cripps insists leaves little time for the kind of administrative tasks that would please Ofsted.

The biter is dismissed just after 2pm and rejoins his class. An hour later, parents gather at the school gate to collect their children. School finishes at 3.10. Next term it will be 3.15. Another five minutes, courtesy of Ofsted.

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