The problem with research into class size is that it is extremely difficult to separate the “class size” effect from other factors, such as social background or teacher competence.

Reducing class size is an EIS policy for which it has understandably campaigned vigorously. If the purpose of the exercise is cutting teacher workload, then this is completely the right way to go and fully in line with the general improvement of teachers’ pay and conditions since 2000.

However, if the purpose is to increase pupil attainment, then things become less clear. The research that smaller class sizes lead to across-the-board increases in attainment is at best ambiguous: the group which has been shown to benefit from smaller classes - the least able and youngest - can be better helped through more targeted use of resources and teacher time.

I refer, of course, to the highly successful literacy programme in West Dunbartonshire. Yes, they have put in extra teachers, but in a targeted way and for specific teachingsupport; they have not spent money on extra classrooms to accommodate a general class-size reduction.

Also, spare a thought for what the current complexity of class size means for children starting in primary school. Gone are the days when the majority of pupils would go through primary school with a relatively stable group of classmates. Now, as the class-size regulations impact differently on different year groups, they may find themselves moving in and out of small classes, and in and out of composite classes.

As constancy is a proven plus in educational terms, such an experience does not augur well for those unlucky enough to be in perpetual motion.

Judith Gillespie, development manager, Scottish Parent Teacher Council.