School league tables are now as old as the 15-year-old pupils whose GCSE results they report.
By Mike Baker
Education correspondent, BBC News
But is it any clearer yet what they are supposed to achieve?
They were created in 1992 by John Major's Conservative government as part of the Citizen's Charter.
The stated aim was to give parents the consumer information they needed to create a free market in school choice.
Since then though, governments have found another purpose for the tables, using them as a lever to direct the school system down one particular track or another.
They have become the Fat Controller's equivalent of the railway signal box. More focus on the 3Rs! Quick pull the maths and English lever. Worried about "coasting" schools. Throw the value-added switch.
The rise of the annual performance tables has been synonymous with greater central direction over schools.
It has proved as powerful a weapon of control as the medieval thumbscrew.
The terrified victims have complained and moaned and have rushed to comply.
The trouble is, like confessions produced by torture, the results have not always been the whole truth.
Take the standard measure of the GCSE tables: five A*-Cs or their equivalent.
It did not take long for some schools to recognise that there were different ways of meeting this threshold.
A few canny pioneers realised that there was a vocational qualification, the GNVQ, which was worth four GCSEs at grade C or above.
Add one more GCSE, in any subject, and, hey presto, you meet the target.
To be fair, many of the original followers of the GNVQ route felt it offered the best educational option for their pupils.
'No hiding place'
Others, though, realised it was an effective way of avoiding the consequences of falling below government targets.
Eventually the government realised that large numbers of schools were achieving the threshold without their pupils achieving GCSE passes in maths and English.
Hence this year's new requirement that the five GCSE passes must include maths and English.
The effects on some schools have been dramatic. One school went from a score of 82% passing the equivalent of five A*-Cs to just 16% when maths and English were included.
Many other schools, which had been climbing up the tables in recent years, found themselves slithering back down again.
Presumably they will now find new ways of targeting performance in maths and English, no doubt at the cost of something else.
'Good or bad?'
Almost since the league tables began, governments have found ways of moving the goalposts.
In 1997, for example, in its first year, the new Labour government warned there would be "no hiding place" for schools that were not striving to improve.
In that year, it introduced an "improvement index" to the tables to highlight which schools had shown steady improvement, or decline, over the previous three years.
Soon after that we had the first "value added" tables - showing the average progress pupils had made while at the school.
The latest version, new this year, is the more complex "contextual value added" (CVA).
This not only measures the progress of each individual pupil but also takes account of other factors affecting achievement, including ethnicity, gender, poverty and special needs.
The problem, though, is that the CVA tables are based on students' best results in any subjects and qualifications. So there was a very sharp mismatch between schools' performance in the maths and English measure and the CVA.
Take the Grange School in Oldham. On the maths and English measure it came bottom of its local league table with just 15% of pupils reaching the threshold. But on the CVA measure it came top.
So is it a good school or a bad school?
Fortunately we can get a second expert opinion as it was visited by Ofsted very recently.
The inspectors judged it to be "a good school with some outstanding features".
Reading the detail of their report, it emerges that the school serves one of the most deprived areas in the country.
The inspectors noted that maths and English lagged behind other subjects but, as a visual arts specialist college, it did well in vocational and visual arts subjects.
So the two, apparently conflicting league table rankings for the Grange School turn out to both be accurate.
Isn't this all rather confusing for parents?
Which measure should we use to judge our local schools: the standard 5 A*-Cs, the new maths and English measure, or the CVA calculation?
The answer is that there is no simple answer. And maybe that is a good thing.
The more the league tables change, and the more complex they become, the more we all realise that these tables give only a partial picture.
When it comes to choosing a school, they are no more than a starting point. Other evidence - Ofsted reports and the experience of a personal visit to the school - will give a much fuller picture.
I am sure we have not seen the last change to league table measurements. For a start, the new Diplomas will soon require further changes.
But perhaps now league tables will be taken with an even larger pinch of salt than before.
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