If there is ever a moment head teachers and school staff feel a shiver of dread run down their spine, it is when word gets around the Ofsted inspectors are in town.

The jungle drums beat out a rhythm of anxiety with a hi-hat of job insecurity. But what actually happens when the inspectors arrive? And just what impact does it have on a school?

“An inspection,” says one secondary school teacher, on condition of anonymity, “can make or break both the school and individual careers.”

Peter Read, a head of Gravesend Grammar for 15 years before running an advisory service for families facing problems with the education service, says: “Hardly anyone I have spoken to ever relishes an Ofsted inspection. And why should they? The only time I’ve heard different was from two heads who knew their schools were outstanding and wanted it verified.”

Ofsted, which stands for the Office for Standards in Education, Children’s Services and Skills, is a government office tasked with ensuring schools are delivering a competent service

Launched under John Major’s Conservative government in 1992, it has evolved over the years and continues to do so – reflecting the political will and focus of the ruling party.

And schools don’t get a lot of warning if they’re next on the visit list.

If a school is going to get an inspection, they will be notified between 10.30am and 2pm the day before.

Then the school has to set into motion wheels which it has, ideally, kept well oiled. Both staff and pupils will be summoned to inform them Ofsted is on its way. Parents will receive an email with a link to a questionnaire on Ofsted’s website.

In short, all constituents are told they can have their say.

If you believe the rumours, some schools even have reciprocal arrangements with neighbouring heads to ship out the most troublesome pupils for the two-day duration of the inspection. All steps to smooth the process are taken.

Adds the teacher: “You can be confident you’re doing a good job and working every hour God sends but, ultimately, it all comes down to the day and ensuring you’re well prepared. I’ve yet to meet any member of staff who actively enjoys them.”

For anyone who knows a teacher, the hours between that call and the following morning are rarely comfortable – the reputation of the institution into which they have poured their heart and soul suddenly teetering precariously.

Ofsted may give the school precious little time to prepare but the inspectors will have already done their homework.

Explains the teacher: “Generally, the inspection team will have studied all the available data on the school they intend to visit in advance – so exam results, pupil progress scores and so on. They then come up with a hypothesis on what they expect to find which they will seek to prove, or disprove, during the visit itself.

“The thing is, it is so difficult to call what they will drill down into. Different inspection teams can have different priorities in what they are looking for. You frequently hear of some schools getting a hard time over one aspect while another, nearby, will barely have to discuss their similar situation.”

Every Ofsted inspection will make judgements on four fundamental areas – quality of education, behaviour and attitudes, personal development and leadership and management. From this, the often-controversial one-word summary will be derived.

They are, as if you need reminding: excellent, good, requires improvement and inadequate.

Kent has fared well. As of last month, a remarkable 92% of the county’s primary schools are either ‘good’ or ‘outstanding’. For secondaries the figures are an impressive 89%. For Medway, the top marks cover 93% of its primaries and 89% for its secondaries.

It is worth noting, however, that some ‘outstanding’ schools have not been inspected for many years. While once practice not to re-visit the highest-rated schools – that has now been changed – it hasn’t stopped some from being overlooked for more than a decade. Tunbridge Wells Girls’ Grammar received its ‘outstanding’ in 2011; Invicta Grammar in Maidstone got its top mark in 2012.

Adds Peter Read: “Most schools have nothing to fear – 90% of schools are told they’re good or outstanding.”

However, the focus on each category is frequently tweaked. Which makes rehearsing for the inspection something that needs regular updating.

And rehearse schools most certainly do. The manner in which preparations take place will vary depending on individual school leaders or academy chain bosses. This can be “deep dives” into individual departments (such as English, maths or science) or full dress rehearsals, with an external team coming to the school – often a squad assembled from elsewhere in a trust with numerous schools – and putting it through its paces.

Those three core subjects tend to be where much of the real Ofsted inspectors’ focus will lie. It is far from uncommon for optional topics, such as art or PE, to simply sweat out the two-day Ofsted probe without seeing hide nor hair of an inspector.

It is a reminder that Ofsted acts on behalf of the government. With the current administration putting major emphasis on the traditional core academic topics, Ofsted’s desire to examine options such as the arts and physical education are, more often than not, next to zero.

“If you're not following the English Baccalaureate,” says Peter Read, “then you're not delivering the goods. It won't get you failure on its own but it contributes to it.”

He says of the secondary schools in Kent and Medway that have failed to hit Ofsted’s standards, for most of them this is because they are in “areas of social difficulty”.

“They should, of course, be able to offer something better for their clientele. But if they do they get clobbered,” he says.

Ofsted believe if you're not following the English Baccalaureate then you're not delivering the goods

“These are things that matter. It's not a consequence of Ofsted – it's Ofsted following government policy. The government says if you're not delivering the English Baccalaureate, you're not delivering the goods.”

The English Baccalaureate (or EBacc as it’s often referred to) is a set of GCSEs the government believes best sets up students for further study and careers. It includes: English language and literature, maths, the sciences, geography or history and a language.

Do not be fooled, however, into thinking exam results are the be-all and end-all of an inspection report. It was once a key determining factor until four years ago – but not any more. Which came as a relief to many comprehensives across a county like Kent where the selective system sees those judged to be best-placed to excel academically creamed off to a grammar.

The inspection team – normally one person for smaller primaries, two for secondaries – will spend the two-day visit carrying out a range of tasks.

Among them is talking extensively to the head teacher about the school’s performance and ethos, as well as other random staff members. They will be quizzed on how they are managed, workloads and views on the school.

One teacher says: “Only the most militant of staff members is likely to be anything but effusive during these interviews. There’s normally a very strong sense of unity among the staff to get through it and show the school – which, of course, we all care about – in the best possible light. You’re not going to conceal or lie about things, but certainly you will focus on all the positives.”

There will also be a chance for inspectors to talk to pupils – often requesting time with a group of children in certain year groups. They will be encouraged to speak openly about how they find the school – whether there is any culture of bullying, the support they receive and so on. It is, one assumes, a heart-in-the-mouth moment for many heads.

Input from parents is also actively encouraged. However, inspectors will also be alert to ‘parents with a grudge’ if the vast majority of other responses are broadly positive, but will be keen to get the comments from all the institution's stakeholders and follow-up where necessary.

Inspectors will sit in on lessons – checking out the behaviour of students while they’re at it – look at exercise books and run through data such as pupil absences and, importantly, safeguarding procedures.

It is not unknown for schools to score highly in all categories but be rated ‘inadequate’ or ‘requires improvement’ if there are serious concerns over learners’ safety, such is its obvious importance.

By the end of the two days, inspectors will meet with the head teacher and provide an overview of what they have discovered. They will also provide an expectation as to what the grading will be. The head teacher was previously sworn to secrecy as to the expected outcome – a stipulation eased by recent reforms in order to ease pressure on their shoulders. They can now share the findings – as long as they make it clear it's only a provisional verdict.

The lead inspector will then bid the school farewell and begin writing up a report with their findings. A draft report will be sent to the school’s head within 18 working days, with five days then permitted for feedback on the report – or, indeed, to challenge it. Once all confirmed, the final report will be with the school within 30 days of the inspection and published online shortly afterwards.

Schools are obliged to send all parents a copy of the report.

These have, over the years, dramatically reduced in size – from detailed reports running to more than a dozen pages to around half of that now.

Each of the four key categories will be graded and, of course, that one-word verdict on the overall rating of the school.

If it’s ‘good’ or ‘outstanding’ then most heads will sleep easy in their beds – ‘requires improvement’ or ‘inadequate’ and they may be facing some tough questions from their governing bodies or academy bosses.

“Surprisingly few heads are displaced as a result,” says Peter Read, “but in terms of your reputation as a head it can be a huge blow – especially if the school was previously rated more highly.”

It can also have some devastating consequences.

In January, Ruth Perry, the head of a Reading primary school took her own life following an Ofsted inspection which saw her school downgraded from ‘outstanding’ to ‘inadequate’.

It threw into the spotlight the pressure such inspections put on the shoulders of staff at our schools – as well as questioning the very mechanism Ofsted is designed to provide.

“I remain of the view,” says the former chief of the Canterbury Academy, Phil Karnavas, “that Ofsted is well past its sell-by date and serves no great purpose.

“An imprecise and clumsy mechanism, it simply cannot do that which it purports to – accurately evaluate the quality of education provided by all schools and provide parents with useful insights so that they can make informed future choices. It cannot accurately evaluate the quality of education for a variety of reasons.

“Schools are different. Schools do different things. Schools do them in different ways. Schools are complex and of different sizes, with different ethoses and different intakes.

“It is a ludicrous proposition that one person, or a handful of people, can acquire enough information, assimilate, analyse, assess, accurately and fairly report it in one or two days.”

But while it has its vocal critics, it is hard to deny the need to ensure that most precious of state-funded practices – the education of our children – needs to have a watchful eye over it to ensure pupils are safe and learning to the best of their ability.

Concludes Peter Read: “You've got to have an independent body check on quality – for the sake of the children.

“If it wasn't Ofsted it would be something else that would be doing the same function. There has to be an inspection mechanism.

“Ofsted doesn't always get it right and I've been critical of Ofsted in several cases but, by and large, it does a good job.”