The National Union of Teachers is considering action to end what it perceives as a “cover-up”, in which staff are stretched to breaking point as they are asked to step in and help teach timetables that do not have a permanent member of staff. The NUT feels it is time to call attention to the single most important prop that is shoring up the educational establishment: professional goodwill.

When I read these reports I feel a twinge of guilt. I am one of the statistics in the twin problem of recruitment and retention. Last summer, after eight years, I resigned from a good school as English teacher and key stage 3 co-ordinator. It seems that teachers are viewed as part of the problem when they are doing their job, and as part of the problem when they are no longer in the profession. It is sad that only in a recruitment crisis are they deemed to be part of the solution. But why are so many leaving?

One reason is work-life balance. In teaching, as in many other jobs, the work is never finished, and the working day becomes a working existence. There is no balance. Teachers frequently talk of the job encroaching on their lives intolerably. At the start of term they stand like King Canute and declare that this time the tide will not come in and overwhelm them. It does, and everyone jokes about “survival”.

But, cry non-teachers, what about the holidays? Surely 11 or 12 weeks of paid leave should embarrass tachers into silence when the rest of the workforce grinds on? But this balance of work and time off has no sensible, healthy rhythm, only a binary existence of “on” for the term, or “off” for the holiday. Many teachers would prefer a balance with less emphasis on stamina.

The term and the academic year have become the proverbial pint pot, into which another quart is annually poured. Curriculums have ballooned into giants of coursework and exam preparation; the regular assessments, reporting and testing (proliferating, as if you could make someone taller by measuring them every day) have become hugely more time consuming.

The traditional structure of the year cannot cope with the demands made on staff and pupils. “Raising standards” has meant “razing staffrooms” in many schools and boroughs. Overspill from the pint pot is the stream of teachers who have had enough.

Schools and teachers have worked within the hard-nosed culture of name-shame-and-blame to bring the education system into line. The aim - to improve children’s experience at school - is clear to everyone. The method, however, is the strangest three-pronged approach imaginable: constant change; an aggressive inspection body; and now performance-related pay that is meant to reward successful teachers and keep them in the classroom.

The Government needs to think how it can keep teachers in schools, let alone the classroom. Money will not be enough. The ratchet effect of increased demands and higher performance criteria is creating tensions that salary cannot adequately compensate.

William Herring lives in north London