Figures from the Department for Education and Employment show that on average, pupil GCSE scores improved by five points between 1991 and 1994 and that the bottom 25 per cent of schools on the league tables have improved the most.
But the results achieved by the bottom quarter of pupils have improved the least (see right) and there is some evidence that the focus of the league tables on the numbers obtaining five GCSE grades A to C is to blame.
As an analysis of the DFEE figures by the education rights pressure group Article 26 points out, the largest increase in GCSE success occurred among the top 40 per cent of pupils who achieved five grade Cs or better (see above).
There is clearly worthwhile improvement. But not everyone is sharing in it. While the scores of the top three quarters of pupils increased by more than the average of five points, the lowest scoring quarter improved on average by less than two points.
The pressure group also pointed out earlier this year that a third of the 52 "improving" schools praised by the Office for Standards in Education for increasing the numbers achieving five or more grades A to C by 10 per cent or more had registered either no improvement or decline in the achievements of lower ability pupils.
Though at least one of the schools involved said it found that the lowest achievers became even more demoralised as improved exam results spread further down the attainment range, there are also some indications that schools are concentrating resources on helping pupils at the five-A-to-C margins.
Targeting this group was certainly the most popular school improvement strategy cited by the 50 schools who contacted The TES in response to a request for details of any school improvement initiatives.
Article 26 is arguing for schools' average GCSE points score to be used rather than the five-grade-A-to-C standard which, it argues, is encouraging the development in schools of "an educational underclass achieving increasingly less in relation to higher achievers".
Certainly it is recognised in the school effectiveness movement that performance measures need to check that different ethnic, gender and ability groups are all benefiting from any school improvement efforts.
In the absence of the average total points score in the performance tables, this argues for more attention to the other, broader indicators, such as the percentage of pupils in a school obtaining five grades A to G or the numbers - and characteristics - of those pupils obtaining no GCSE grades at all.
Rather than competing on unequal terms with higher ranking schools in the five grades A to C stakes, some schools might even find it easier to promote themselves as schools serving the whole community by enabling every child to succeed, regardless of ability.