Dear Tony Blair, What were you doing in Switzerland in 1981? You must have been there, because one of New Labour’s recent advertising posters clearly borrows from a Swiss supermarket’s proud boast of the period.

Roughly translated, its posters, supposedly testifying to the freshness of its stock, declared: “If you see an item past its sell-by date, it’s yours with our compliments.” Hapless student that I was, I scoured the shelves for free food until I realised the substance of the poster’s message was far less generous than the tone.

At first glance, the smiling grandmother on your poster testifies to an unqualified achievement. “450,000 children in smaller infant classes. I did that,” she says proudly. Yes, there are winners, but there are also losers.

Wait a minute. On closer inspection, I see that your grandmother’s words are an apology. So for the benefit of all those parents too exhausted to read between the lines of your campaign poster, here is that apology in full - sorry, make that apologies. Just sign and send.

Dear (insert name of child in an infants’ class - you can start with my daughter), You know just how long and lonely playtimes in a new school can be. Telling you to look for your classmates isn’t much help when you can’t see above the heads darting around you.

You finally found a firm friend, in your class, and the only lunchtimes you then feared were those when she was off school. But thanks to my policy of reducing class sizes, you have been separated. She is now in a different class - a higher year group. So you have to look for new playmates all over again. Hope you find some soon.

Dear (insert name of teacher who must now teach two age groups in one class), Just when you thought you’d cracked the literacy and numeracy hours, along comes a phenomenally wide ability group. Remember that some primary teachers have three or even four age groups in a single class, so you’re lucky really. Just think of your new challenge as professional development of the highest order.

Dear (insert name of parent who lost appeal to get child into local, oversubscribed school), Our reduction in size of infant classes created more places in some opular schools. I am sorry you could not afford to move closer to the school of your choice to guarantee your child a place, but your child will now be in a smaller class so will receive more attention and attain even higher standards.

As for the allegation that sending my two sons miles across town to the London Oratory school has deprived two local children of places, it is not for me to interfere in a school’s decisions. Clearly my sons are better suited to the school than others living closer. Such diversity of educational provision is a cornerstone of our educational policy.

Dear (insert name of headteacher of unpopular school which has seen reception rolls fall), Welcome to smaller classes. I know your lower pupil numbers mean reduced funding, and realise you may have to make some redundancies. But I am confident that you can make these in the most effective way possible.

I am sure you can dispel the myths that the majority of children who would once have joined your reception class, but will now go elsewhere, are from the most supportive families, and that your staff will be demoralised by the lowering of the overall levels of attainment and conduct of infants joining your school.

In short, Tony, I know smaller classes have some advantages. But I have taught secondary groups of 33 and of 13. I know that 33 biddable pupils receive far more attention than 13 who include children with major problems who take up so much time the rest of the class barely gets a look in.

Thousands of parents would move heaven and earth to get their children into classes of 50 in popular schools where they know children can learn, rather than let their children join far smaller classes in schools with more than their share of problems. Please put the money where it is needed most, not where it wins most votes.

The only hope for children in difficult schools is for more highly gifted and experienced teachers, to ensure that every child can learn, whether in a large group or one-to-one. Forget realpolitik. The real question is not:

“How do we get more of those who bother to vote to vote for us?”, but: “How do we get far more of the very best teachers into the most difficult schools?” Now that would be something to be proud of.

Jenny Owl is a pseudonym. The writer is a head of department