'I know we are terrifying – but we're not bully boys'

They're hated by teachers yet rarely defend themselves in public. So what's it like being an Ofsted inspector? Richard Garner meets one

They stalk the corridors of schools, striking fear into the hearts of even the most senior teachers. They are the Ofsted inspectors – but until now their voice has seldom been heard. In a rare interview, one of the education standards watchdog's most senior inspectors has given i an insight into the nature of his work, which under the regime of Ofsted's new boss, Sir Michael Wilshaw, is about to get a whole lot tougher for schools.

As a former primary school head, Mike Sheridan speaks with experience about the impact an inspection can have on staff. "It's quite terrifying," he admits. As a poacher-turned-gamekeeper, he now leads an Ofsted team and makes up to 33 inspections a term.

He immediately rejects the image often put forward at teachers' union conferences of Ofsted acting as "bully boys" bringing a reign of terror to schools. The inspection, he says, will usually start with a telephone call to the headteacher 48 hours ahead. With a day to go, he contacts them directly.

"We'll go through the data on the school and make sure everything is as accurate as we think it is," he says. "Hopefully, the headteacher will be able to challenge anything that could be wrong." They then go through the issues that need to be looked at when the inspection starts.

But before he heads for the school gates, he goes online to look for candid comments by parents, usually focusing on the controversial forum Parent-View, where mums and dads can post comments anonymously about their child's school. The website angers teachers, who say there is no accountability or even any way of telling if the user is a parent at all. They claim that ParentView, and other sites like it, are open to abuse by people with an axe to grind. But for an Ofsted inspector it is a useful guide to the problems they may encounter on a visit.

When he arrives, he immediately gives out 100 questionnaires to pupils (parents are often sent these ahead of time, too). Children's comments are not treated as gospel, but the survey almost always earns a 100 per cent response. "The information can be quite telling," Mr Sheridan says. "You get some traits in there which lead to interesting discussions. Parents' views are taken very seriously."

He will then schedule a meeting with teaching staff. "It is a very stressful time for schools, and we know that, and we do everything we can to make it as simple as possible," he says. "When I was a headteacher, you had six weeks' warning of an inspection – I can remember waiting by the telephone when you thought it was about time you were going to get the call."

He adds: "The teaching profession is a real mixture of people. Most teachers are incredibly passionate about what they do. They are working incredibly hard and they do deliver. Not all do it absolutely right, though. What I say is that when we are making judgements about teaching and learning, we're not making judgements about individual teachers. It would be madness to do that in a 20-minute slot. Teaching a satisfactory lesson for 25 minutes doesn't make you a satisfactory teacher."

Mr Sheridan is not alone in making the jump from teaching to inspecting. Most full-time inspectors have been heads or senior managers in schools, or have worked in education authorities. About 40 per cent of inspectors, who are recruited from all walks of life and were once dubbed by teachers' leaders "the butchers, the bakers and candlestick makers", are still teaching.

During the course of the day, Mr Sheridan will make six or seven lesson observations, before returning the next day to complete the inspection. Almost all of a school's teachers will be observed at some point. He will then withdraw with his team and spend up to 90 minutes talking through their judgements with the head, who can challenge the findings – an important process, he says, as it "adds to the transparency of the inspection".

Since joining Ofsted, he cannot recall any of his team's judgements being challenged. But the inspection system is braced for major change, with Sir Michael due to unveil a blueprint for the future. His plans include the introduction of "no notice" inspections, replacing the "satisfactory" rating with "requires improvement", and failing schools which fail to lift themselves out of that category within three inspections. In effect, the new regime says that if yours is not a good school, you could be on the road to failure. It will also limit the number of schools rated as "outstanding", making it more difficult to qualify.

Ofsted, Mr Sheridan says, has to work "without fear or favour". But will that be possible under the new system? "We have ways of making things work," he says. "Whatever comes out of the consultation we will work with it."