Every school in this local education authority which has introduced a system of classroom observation before an inspection has retained the system afterwards,” says the senior local education authority adviser, trying to persuade us that our school needs this increasingly widespread tool of school improvement.

His words remind me of an extract from a report by Her Majesty’s Inspectors on inner-city schools. It said: “The head (at my then school) has, with the backing of staff, introduced a system of classroom observation.” While this comment and the LEA adviser’s remark sound perfectly plausible, both hide important facts.

Most systems of classroom observation continue post-inspection not because they work, but because they show that the school is “doing something” to address the issue of school improvement. As for the HMI quotation, it included a lie - the staff did not back the system. In fact, its most significant effect was to severely demoralise us in what was already a difficult school.

I like to think I was able to be objective about the system because I was its co-ordinator. I conducted classroom observations, wrote the reports and fed back to individuals and departments. A year after we had introduced the system, the head, to his credit, asked me if classroom observation had actually improved the teaching within any department. I had to say “no”.

Ironically, though, it united the most dysfunctional department. Colleagues who previously had talked to each other only to express frustration at the lack of support from their head of department, suddenly rallied round her to pick holes in the final report on their observed lessons and to justify an alarming lack of departmental discussion, planning and student support.

On the positive side, it was wonderful to observe great teachers in action, to tell them so, and to encourage them to invite others to watch their excellent practice. Watching such colleagues also forced me to confront my own failings, and improve my teaching.

While I have learned more from observing others teach - and from post-observation feedback on my own lessons - than from anything else, I am alarmed by the extent to which the Department for Education and Skills and LEAs encourage senior managers on to the observation bandwagon. Because of the pressure to improve results, it is all too easy for senior management teams to transfer the pressure to teaching staff without improving the quality of teaching.

On the face of it, a teacher whose class’s exam results show that significant value has been added to pupil performance is an above average teacher. Conversely, a teacher whose pupils’ results demonstrate negative added value is below average. I have been both kinds of teacher in the same school. The group I “taught well”, as shown by their GCSE results, was not only very biddable but, significantly, joined the school when the senior management team promoted a strong school ethos. Two years later, with a far weaker senior management team, another group I taught, with more than its fair share of difficult students, significantly underachieved at GCSE.

The major flaw in the Chris Woodhead response to my results with the second group is that it would condemn my teaching without addressing the fundamental question: “How do we as a school help this teacher help a difficult group of students?” An honest answer would recognise that the senior management team needed more authority, some of which would rub off on me.

The present culture of blame discourages honesty and, worse, destroys any hope of creating the climate of trust so crucial to classroom observation and improved teaching. The classroom observer who has won the trust of colleagues has the greatest chance of helping them develop professionally.

My belief that I will only ever be supportive of colleagues is irrelevant: all feel understandably threatened by the possibility of my incursion into their classroom. Although I have extended an open invitation to colleagues to drop in to my lessons unannounced, none has taken up the offer out of consideration for my likely self-consciousness at being unmasked as - most of the time - an average teacher. In short, trust takes a long time to build, and true school improvement can only come about through classroom observation managed by colleagues who have the trust of the whole staff.

Jenny Owl is a head of department in the north of England. She writes under a pseudonym