Dear Tony Blair

I am an outstanding teacher. I added an average of 1.5 GCSE grades to those predicted for my Year 11s the year before last. I deserve every penny of the pound;2,000 available to those who cross the pay threshold.

I am a lousy teacher. I added an average of - 0.25 of a GCSE grade to the predicted grades of my Year 11s last summer. Same teacher, same school. Why the difference?

I had a good relationship with the first group, which had only a couple of difficult pupils, while the second included many disruptive pupils and was harder to teach. How meaningful is any judgment of my “performance” with either group?

Many factors beyond the control of an individual teacher affect results, yet results strongly influence whether an individual crosses the performance threshold. I still remember a throwaway remark made by a colleague at the school in which I trained. “He hogs all the top sets,” she said about our head of department. Performance management positively encourages such abuses of power, just as league tables encourage unscrupulous - or just plain desperate - heads to concentrate resources on students on the five GCSEs A*-C grade borderline.

I breathed a huge sigh of relief last summer when I finally deposited my completed threshold application in the head’s in-tray. Little did I know that, six months later, I would be devoting considerable energy to working out what on earth our threshold assessor wanted. You see, a departmental colleague has just been told that he is among my school’s sample of threshold applicants to come under the assessor’s scrutiny. He has not slept since.

Like me, he read the account of an English teacher’s humiliation, anger and hurt (Talkback, Friday magazine, January 12) at being failed by the threshold assessor: “The head felt that I met the criteria, but the assessor, after his lightning visit, failed me.”

Doing a good job is about doing a good job, not trying to prove to someone who does not know you from Adam that you do a good job. Suddenly, you have to forget the job and concentrate all your efforts on proving that, to use the threshold application form jargon, you are at least “as good or better” than sliced bread. It is all very well David Blunkett referring to crossing the threshold as “promotion”, but which other grup of 200,000 people has ever had to:

* apply for the same promotion simultaneously?

* bear in mind that not applying would result in many people - including the governors who appointed them - interpreting this as meaning that they were not effective employees?

* endure a humiliating scrutiny - allegedly scientific, but in practice far from it - many months after completing the application form?

Since learning that he was to be scrutinised by the assessor, my colleague says he’s at an all-time low. I know he is a very good teacher. Our head knows he is a very good teacher. Yet we are all going through various stages of hell wondering how we can persuade the assessor that he’s a very good teacher. You trust heads to appoint for life, you trust them with annual budgets averaging pound;2 million in secondary schools, yet you do not trust them to decide whether a colleague who has taught for many years does a good job.

I cannot generalise, but I assume that most practising teachers lack the time to be assessors, and that many assessors will have left teaching because they could no longer hack it. I know our school’s assessor. He is a decent person. In a previous life I saw him teach a lesson that Ofsted would have failed. Even more worryingly, I believe he did not realise this. Should I take heart and assume that he will give all our threshold applicants the benefit of the doubt? I would love to. But, from what he has told our head, it seems likely he’ll fail some applicants.

So, Tony, is it really a good idea to reward the vast majority of teachers while recognising that you will unfairly fail to reward a minority, and destroy any vestiges of the latter’s self-confidence into the bargain? Lord Puttnam, who has worked hard to raise the status of teachers, has expressed surprise at our low self-esteem. You, Tony, tell us - at least if we teach in inner-city comprehensives - that we are “saints”. Presumably because humiliation goes hand-in-hand with sainthood. Your government trusts us so little that it made 200,000 of this country’s most experienced teachers spend our half-term last summer justifying a pay increase; and trusts headteachers so little that you send in a team of dubious ability to pick holes in our applications.

Accountability I can handle. But this is sheer, unadulterated humiliation.

The writer, who uses a pseudonym, is a head of department