Composite classes are an important feature of Scotland's primary education system. For generations, many small rural schools have made a virtue of necessity and younger pupils have benefited from the role models offered by older ones and from techniques such as cross-age peer tutoring. Today The Herald reports that many urban primary schools are having to resort to two-stage classes in order to implement the Scottish Government's targets on class sizes in the first three years.

Worthy policy aspirations sometimes have unintended consequences, especially if they are not properly resourced. This seems to be a case in point. The target of a maximum of 25 per class in P1 to P3, reducing ultimately to 18, will mean some children progress through primary school with the comforting continuity of their own cohort around them, while others move in and out of composite classes. This perpetual change is not likely to be popular with parents and some children may find it hard to settle. It seems unlikely that parents would prefer a composite class of 25 in a school they did not choose to a class of 27 in their chosen school. It stands to reason that children will do better if they have more attention from their teacher but the extent to which slightly smaller classes benefit children remains a topic of debate. The evidence is at best contradictory. Other factors, such as the quality of the teaching and the presence or absence of disruptive pupils, are at least as important.

If the Scottish Government wants smaller classes, it must resource them properly. At present it seems willing to fund the training of extra teachers while not giving councils enough to employ them. Last week The Herald reported that fewer than a quarter of last year's probationary teachers have found permanent jobs. The Association of Directors of Education Scotland estimates that councils need £62m extra to employ the additional teachers required to implement the policy on class sizes, as well as £360m to build new classrooms.

Composite classes have their place but in this instance their creation is not driven by the best interests of the children. There are no sound educational grounds to justify this change. There is a difference between what is good for children (and acceptable to parents) and policy driven by political dogma.

The issue of class sizes is shaping up to become the biggest test of the so-called concordat between the Scottish Government and local authorities. With the legal limitation on class sizes unchanged at 30, parents are successfully challenging in the courts refusals to admit pupils to classes of between 25 and 30. There is a suspicion that the law remains unchanged because the government knows it does not have the resources to implement it properly, leaving local authorities to adopt "make do and mend" alternatives. Could composite classes become the subject of court action?

Smaller class sizes are a laudable aim but, unless they are properly resourced, the policy may be simply unworkable.