Generals are always accused of preparing to fight the last war, rather than the next. An illustration lies in the construction of, and futile dependence on, the Maginot Line, that huge complex of fortresses and tunnels that was built on France’s eastern frontier during the 1930s in order to deflect any German advance while allowing the French army time to mobilise. That would have been great to have in 1914: in 1939 it was a self-deluding disadvantage. Instead of attacking it, Hitler simply chose to go round it. Even those of us who would rather not see any wars know what the criticism means. However, there is a corollary to this view. It points to the fact that we are often too ready to move on to new problems without solving old ones and that is where we may be in relation to the issue of class sizes.

There are some who have begun to suggest that the desire for smaller class sizes throughout the school, and particularly in the early years, is old hat (TESS, June 18). “Flexibility” is the new buzz word, and with flexibility (by definition) anything can happen. The curriculum can vary, the organisation of learning groups can be revolutionised, personal plans can come to the fore and teachers can even start to teach again.

Accordingly, that is the holy grail we should seek.

In this analysis, teachers who continue to argue for smaller class sizes can easily be dismissed as being old-fashioned and a trade union that ballots its members on the issue can be sneered at for being Luddite. But, to continue the military analogy, I would strongly advise those who are still arguing for smaller classes to stick to their guns. A radical change in accepted class sizes, far from being an idea whose time has passed, is one whose time has not yet come. Moreover, without succeeding in this campaign, it would most probably be impossible to introduce the very flexibility which is now so much in vogue. There is nothing intrinsically wrong with the Executive’s plan to reduce S1 and S2 maths and English classes to more appropriate sizes, although from the very beginning it was obvious that it would be hard to do.

Maths teachers, in particular, do not grow on trees, and how an existing shortage was going to be turned into the necessary surplus was never explained far less thought through.

But even if this could be done it would leave other vital areas of schooling untouched. There is absolutely no doubt that maximum sizes of less than 20 in the early primary years are of the utmost importance in terms of subsequent attainment as well as subsequent behaviour.

If I do not call into evidence the many well-studied examples around the world to make the case, it is only because it is now self-evident and has been since it was first seriously discussed in Scotland at the end of the Second World War. But we should go further. Sustaining those smaller class sizes through the entire primary school is almost as worthwhile in terms of results and certainly as worthwhile in terms of teacher satisfaction and the quality of teaching possible. In secondary, having smaller classes also accelerates learning, helps meet social inclusion aims and improves teaching morale.

The important issue is how to do it, and where the money can be found. Here the demographic realities become very helpful: the number of teachers projected by the Executive is actually due to fall in the next 10 years as the number of pupils falls - simply maintaining the present establishment (largely by training more primary teachers ) will go some way to producing the right balance.

Medium-term financial projections for education therefore need to be revised with that aim in mind, and supplemented as required. The outcomes are so positive that this should be treated as an ultimately self-sustaining investment, a concept that requires to be inserted into much official thinking, given the present extreme short-termism. An increase in training places is also likely to be self-sustaining, particularly if there is radical thinking about how training is done.

Given the desire to renew or refurbish most school buildings in the next two decades, putting in place the absolute requirement to meet new maximum class size targets in all accommodation due to come on stream may stretch the budgets a little, but it will not break them.

The argument that modern schooling requires new buildings, which is made much of by directors of education hell-bent on closing schools, will continue to be badly skewed if it does not take into account not just better facilities and equipment but smaller and more effective teaching environments.

Taking these elements together, what is needed is the political commitment, the civil service plan and then the allocation of funds over a sustained period. This is exactly the approach taken, for example, in Quebec, when a universal system of childcare and pre-school education was introduced over five years. Ten years would be about right for this initiative.

Those who know the cost of everything and the value of nothing will no doubt continue to argue that it cannot be done. That is a dangerous argument in a country that has just found out that its government has underspent by almost pound;2 billion in less than five years. It is also a curious one, at a time when it is regularly officially contended that only the best education will result in a flourishing economy.

One of the reasons that the Maginot Line failed was because the plan was not ambitious enough. To solve some of the problems of Scottish achievement, we have to think big and be prepared to put our money where it can produce the best results. No doubt flexibility is part of that, but the foundation has to be a reduction in the size of the units that teachers face every day.

Michael Russell is a writer and broadcaster.