There is nothing sacrosanct about any particular type of school, whether state or independent, comprehensive or selective grammar. In essence, there are good schools and there are bad schools. From the annual desperate clamour of parents seeking to get their children into the school of their choice, and hoping not to hear that they must instead attend the school they least favour, we see they cannot be fooled – they know what a good school looks like.

So I will not pretend that all high-achieving schools must automatically be “good”. Indeed, it should not come as a shock that Stretford grammar school, in Trafford, Greater Manchester, with a 96 per cent pass rate at GCSE has been put into “special measures” by an Office for Standards in Education (Ofsted) inspection team and labelled a failing school. What is perhaps more disturbing is the inspectors’ judgment that although academic standards were “exceptionally and consistently high”, they felt that the curriculum in some non-academic subjects was “inadequate”. Not surprisingly, defenders of selective schools have condemned the government as being hostile to grammars.

In recent years, armies of statisticians have emerged to try to tell us what we all know – that a good school is not just a school with solid examination results. Instead, they tell us we should make our judgment on the statistical shibboleth of “value-added”.

New Labour’s obsession with mechanistic targets has reified this as the golden braid from which all true measures of excellence can dangle. The pupils enter the gates of their new secondary schools tagged with “measures of prior attainment”, albeit based on spurious, contentious and unreliable data from their Key Stage 2 SATs. If you are not “in” education, or do not have a child currently within the quagmire of modern schools, you will already have been lost to the obfuscating terminology that embraces education with a life-stifling grip. It is a world in which Shakespeare is best studied by reading only the scenes that are to be examined and skipping the rest as irrelevant. It is a world in which spirituality is measured out in the number of assemblies or minutes spent in a PSE (personal and social education) programme and in which governments proudly announce campaigns to tell schools that “every child matters”. It is too often a world presciently described by Dickens as one from which “springs…the mechanical art and mystery of educating the reason without stooping to the cultivation of the sentiments and affections”.

And the ultimate measure of the mechanical art is the arrival of the Ofsted inspectorate. I have to confess that my own school is not typical: it is one of a dwindling number of grammar schools. It must, by most measures, be rated among the top state schools in the country, even though we frequently admit pupils not from the top two per cent of ability but from the top 25 per cent.

We have nothing to fear from the inspectors, especially as, because of our success, we were assigned a mere one-day quickie inspection. Nevertheless, all of the staff were geared up and ready for the day, genuinely anxious to display just how good the school is. The pupils too, even the most recalcitrant, were determined that ranks would be closed against any outsider daring to criticise their school.

Unfortunately, there was one small exception to this unification of the troops and that was the tiny minority of parents who had their own particular axes to grind. So, the school had refused to move their child to a class with their best friend, or had been unable to provide their child with the precise subject options that they would have preferred, or the school had, without any grounds at all, complained about the conduct of their allegedly perfect offspring. Whatever the specific cause for their festering resentment, this they saw as a chance for revenge. No matter that they would not consider letting their child leave for an “inferior” school, they still felt, fortified by all the talk of parent power, determined to exact some personal retribution.

All parents are sent a benign and anonymous questionnaire by the inspectors. We were pretty proud at the unusually high response rate, demonstrating, as we naively supposed, the overwhelming support of the parents. Indeed, it showed overwhelming support – apart from the minority of complaints. To our astonishment, frustration and growing anger, we found that a disproportionate amount of the day was spent feeling like suspects answering to anonymous accusations about our bad practice.

The first signs of abnormality came early on. One of the events of the day coinciding with the inspection was a long-planned workshop for talented keyboard players to develop their skills further and to work together to learn new techniques. The inspector, who on the telephone had claimed to be a great lover of music and proud of her own musical family, breezed into the session and stayed for 30 seconds, saying she had other things to which to attend. We are particularly proud of our excellence in choral work and one of our choirs was rehearsing at lunchtime. The students were told that they would be visited and, rather than end the rehearsal in time for sandwiches, voluntarily stayed on to practise. But no visit came. The inspectors clearly had more pressing concerns than being courteous and interested enough to listen to pupils proudly displaying their excellence.

We were allowed to see one of the complaints. It was a three-page diatribe so ludicrous that no sane person would have treated it seriously, including, for example, the allegation that teachers were openly allowing drug-taking and boasting of their own criminal records.

On a more predictable level was the handful of parents complaining that the pupils were made to work too hard. The inspectors, in their interviews with students, found no grounds to substantiate this odd claim. At one point, the lead inspector said that some parents thought the pupils were unhappy. This remark was spoken over the sound of pupil laughter in the corridors – they had not read the script.

It became more and more apparent that beneath the investigations of trivia there was resentment against a selective school being so successful and providing an education that was producing independent-minded young people with the talents and qualities to make a difference in the world. There was, in short, a suspicion of “excellence” and, at the end of the day, when it proved impossible not to grade the school as “outstanding” in every single category, the final summing-up included the gleeful words, “but only just”, with the inspector’s thumb and index finger pinched together to indicate how grateful we should be for her concessions.

After they had departed, my colleague remarked that it felt like winning the FA Cup and going home thoroughly depressed by the experience. We had got the result we deserved, but felt that far from recognising the genuine values being added by the enthusiasm and experience of our hard-working staff, we were instead being assessed only on a set of outcomes, the numbers of examination passes that “proved” we were outstanding at teaching children to pass examinations. What joys Orwell would have had with the concept of “value-added”.

Of course, I know that we are an outstanding grammar school, providing pupils from a huge range of social backgrounds with a secure foundation in the love of learning. I also know that some of these pupils would have struggled and almost certainly “failed” in a “bad” school. Yet in 20 years’ time will they be saying, “I am so pleased that my school provided such a great non-academic curriculum – oh, and did you know that it achieved +0.48 as a value-added score”? Or will they be more likely to regret never discovering that love of literature, that facility with numbers, that passion for science which would have made them a truly educated person?