A third of the 52 improving schools praised by the Office for Standards in Education have registered no improvement or a decline in the achievement of lower-ability pupils.
The figures may provoke concern that schools have concentrated on boosting the well-publicised figures for grades A to C - usually seen as a pass by employers and university and college admissions officers - at the expense of struggling pupils.
The 52 schools were listed in this year's Chief Inspector's report, a new departure. All had GCSE improvements of 10 per cent or more, and had good inspection reports. But an analysis of the schools' other results by Article 26, an education pressure group, reveals that 17 show increases in the number of pupils leaving with no GCSEs, even at grade G. Six have also seen a drop in the number getting five passes at grade G (or better).
In the case of one school, Anfield community comprehensive in Liverpool, the proportion of pupils leaving with no GCSEs rose by 11 per cent between 1992 and 1994. At the same time, their higher-ability pupils were recording a large improvement in passes at grades A to C from six to 18 per cent.
Parkside comprehensive in County Durham registered a 5 per cent increase in the number who achieved no GCSEs; despite a 13 per cent jump in the number of those getting five A-C grades. Headteacher Jim Jewell said: "All of our kids are as important as each other."
Charles Bell, who runs Article 26, said that the improvements among the average and high achieving pupils may be diverting time and resources away from socially disadvantaged groups.
Professor Peter Mortimore, director of London University's Institute of Education and the leading figure in school effectiveness research said, "I applaud the celebration of success. But it's always difficult to ensure that the choice is fair. Schools need to focus on the whole range of pupils. "