The decision of the Information Commissioner to authorise the release of Leaving Certificate data for each school raises serious issues for the educational system as a whole. The commissioner argues that he has "made no judgment as to how the public interest would be served by releasing the information concerned". However, the decision is likely to be highly damaging to the public interest.

It is clear that the newspapers involved in the application to the commissioner intend to use the information to compile a "league table" of schools similar to those compiled in Britain.

What can such a table tell us? There are significant differences between Irish second-level schools in their Junior and Leaving Certificate performances, as my study, Do Schools Differ?, illustrated. However, there are also real differences between schools in the kinds of pupils they have, in terms of their social class, ability and gender mix.

There is a fairly high degree of active school selection on the part of pupils and their parents; around one half of Irish pupils do not attend their nearest or most accessible second-level school.

This selection results in differences between schools in the nature of their pupil intake which naturally affects their final exam results. Most differences in exam results between schools are, in fact, due to differences in their pupil intake. Therefore, knowing a school's raw exam results tells us little about what a school itself contributes to the education and welfare of its pupils.

Ranking schools in terms of their raw exam results can give a very distorted impression of school effectiveness. A school may rank highly in a league table merely because it has a selective intake, drawing pupils with higher abilities and from more privileged social backgrounds. On the other hand, a school serving a more disadvantaged pupil intake may appear low down in a league table but may actually be achieving great academic progress with its pupils.

When we take account of pupil intake, the ranking of schools changes completely. Some schools that appeared to be high-performing in terms of their raw exam results are, in fact, only doing as well as can be expected given their selective intake.

Taking account of the type of pupils in a school means we can measure the "value added" by the school; that is, the difference a school makes to the educational progress of its pupils relative to their initial ability levels. The publication of a league table of schools will not indicate the "value added" by the school, but will instead give a highly misleading impression of how schools are faring.

Decisions by the commissioner are required to take account of reasonable expectations of the anticipated harm arising from the release of information. The publication of a league table of schools is clearly likely to have damaging consequences for the school system as a whole. It will do most damage to the many effective schools serving more disadvantaged areas throughout the State.

School management, staff, parents and pupils in these schools are likely to be disheartened in spite of the positive differences they are making to the lives of their pupils. This is likely to hinder the real advances that have been made in recent years in developing provision for schools in disadvantaged areas and in nurturing links between schools and the local community.

The commissioner argues that "there is a possibility that the granting of the present request would make more accurate information about academic results available to parents". However, it would, in fact, make inaccurate and misleading information available to parents. It does not tell parents how their child is likely to get on in a particular school, merely how previous pupils, who may be very different from their child, have fared.

The British experience has indicated that parents often respond to information from league tables in selecting schools for their children. Parents have actively sought to avoid those schools labelled as "sink" or "failing" schools, with the result that schools have become more and more polarised in social terms. There are good reasons to believe this is possible in the Irish context. And this trend may become accelerated in the face of overall decreases in pupil enrolment and increasing competition between schools for pupils.

More broadly, ranking schools in terms of their raw exam results gives a very narrow view of education. What do we expect our schools to accomplish with their pupils? Is academic performance the only goal of the educational system? Are we just concerned with boosting "average" performance or are we concerned with inequalities in educational performance?

Should we also be concerned with preventing pupils from dropping out of school and with the broader intellectual and social development of young people? A narrow league table approach means that we ignore these other important goals of schooling.

Instead of ranking schools in a crude league table, it makes more sense to focus on developing the school characteristics that promote pupil achievement. Pupils tend to do better in their exams where they are involved in the school and have more flexible subject choices, where the disciplinary climate is "strict but fair" and relationships with teachers are good, and where their teachers hold higher expectations for them.

On the other hand, streaming (grouping pupils into classes on the basis of their assessed ability) tends to have highly negative effects on performance for those allocated to the "bottom" classes without securing any gains for those in the "top" classes.

In policy terms, it would make more sense to promote good practice among schools in Ireland along these lines rather than pitching schools into a competition that nobody can ultimately win.

Dr Emer Smyth is a research officer with the ESRI. She is the author of Do Schools Differ?, an analysis of how schools influence exam performance