In other respects the timing of the report - immediately before the announcement of government spending plans that ministers hope will demonstrate that education is not underfunded - suits Gillian Shephard very well. The content does too. It is only six months since the Secretary of State for Education and Employment was overheard to say that she did not need to see any more research on the effects of class size. But she is no doubt happy to make an exception in this case.

Chris Woodhead, the current bete noire of the teaching profession, has emphasised that the decision to carry out the research was his alone, but his critics will take some convincing. Many teachers, still smarting from Mr Woodhead’s allegation that there are 15,000 incompetent teachers, will see this report as confirmation that he has seriously compromised the jealously guarded independence of the inspection service (the title, Her Majesty’s Inspectorate, was chosen to underline the inspectors’ detachment from central government). They may welcome his comments about the anomalous school funding system but will be irritated by many other aspects of this report, particularly the insinuation that some primary teachers and heads may not be spending enough time in the classroom - a point that Mrs Shephard has also made. “A future OFSTED investigation might usefully focus on the range of duties undertaken by teachers and the actual hours spent teaching,” the report says.

Nevertheless, it has to be said that the report’s central argument - “Except in the early years, reductions in class sizes of one, two or three are not likely to have an educational benefit which justifies the increase in public expenditure” - is one that has also been repeatedly advanced by leading academics such as Professors Peter Mortimore and Michael Barber. Barber, a former National Union of Teachers’ official, has argued that if more money were to be allocated to education some of it should be used to reduce infant classes but the rest should be spent on professional development.

Teachers have never been so sanguine about large classes, of course, and they will have been encouraged to hear that Duncan Graham, the former National Curriculum Council chief, has confirmed that the new curriculum was really designed for classes of about 25. It is understandable that they should be concerned about current pupil-teacher ratios which are the worst for 15 years. It is also true that the standard classroom was not designed to accommodate the bumper classes that many schools are now seeing. Introducing more classroom assistants, as OFSTED advocates, is therefore not always the best answer. In any case, valuable though they are, the assistants also need to be supervised.

As far as teachers are concerned, of course, the simple, undeniable truth is that large classes mean more work and stress, and this fact is partly recognised by OFSTED which says research shows that teachers in classes of fewer than 21 children work three hours less per week than those supervising classes of 26-30 (46.4 hours compared with 49.6 hours).

Under those circumstances, teachers have been relatively restrained about the growth in class sizes that has resulted from an influx of 120,000 extra children this autumn. Members of the Association of Teachers and Lecturers have been ignoring their union’s advice to refuse to teach classes of more than 31 for more than two consecutive days (that was never a practicable proposition). The National Union of Teachers and National Association of Schoolmasters and Union of Women Teachers, despite all the shouting and posturing at the Easter conferences, have kept a low profile too, fearful that they might lose the support of parents and governors.

The Government cannot afford to lose the support of that constituency either and there is no doubt that Mrs Shephard reminded her Cabinet colleagues of that fact during the recent series of public spending meetings that apparently resulted in an extra Pounds 800 million being diverted to education. Like the chief inspector, Mrs Shephard may believe that there is no pressing educational argument in favour of reducing pupil-teacher ratios. But when parents are marching against large classes in central London and families in traditionally Tory Thameside villages such as Goring are pulling children out of classes of 40-plus she cannot be seen to be sitting on her hands. When it comes to politics, class size matters a great deal.