Madam, - A recurrent theme in debates about education here - and one particularly to the fore at this year's teachers' conferences - is the reduction of class sizes. The unions argue for it, the Minister has indicated support for such a move and the Programme for Government contains a commitment to it. We are reminded that class sizes in primary schools, at an average of 25, are higher than the EU average of 20.
It might be reasonably assumed then that there is good scientific evidence - as distinct from anecdote and folklore - that large class sizes are a barrier to educational success. Why, then, is such evidence not cited? Largely because it does not exist, at least for Ireland.
The best source for Ireland is the Programme for International Student Assessment (PISA) collected by the OECD. Its report, published in 2001, shows that pupil-teacher ratios do not have a statistically significant effect on students' performance in reading, science or mathematics. Only at very high ratios (35+) does there appear to be a negative effect. The arguments for reducing average class sizes should be distinguished from the question of how best to help pupils with special needs.
If one takes the Irish data by itself there is a strong positive correlation between students' performance and class size - i.e. students in larger classes do better on average. This does not imply that increasing class size would be better for students because there may be confounding factors, but it certainly does not imply the opposite.
Given the paucity of evidence for Ireland, it makes sense to refer to the international research literature since the effect of class sizes and other school characteristics have been widely studied, especially in the US. A review of the literature by leading UK researchers in 2002 found that in developed countries improvements in school quality are minuscule or-non existent. The Scottish Office recently commissioned a study, "Skill policies for Scotland" (2005), co-authored by James Heckman, a recent Nobel Laureate in economics at the University of Chicago and a leading expert in education research. It concluded that "pouring more funds into schools to lower class sizes by one or two pupils or to raise spending per pupil by a few hundred pounds will not solve the problems of the Scottish primary and secondary educational system nor will it stimulate the college-going of the poor".
If your doctor prescribed a treatment for which the scientific evidence was equally poor, you would be entitled to feel extremely nervous. Of course, the authorities would not license such a treatment in the first place. Educational reform should be no different and is too important to be based on assumptions that are either untested or rejected and ideas that have not been well thought through.
If policy is not to be evidence-based, what is to to be based on? - Yours, etc.,
Dr KEVIN DENNY, Geary Institute, University College Dublin, Dublin 4