Up to the 1990s, A-level grades followed the classic bell-shaped distribution curve, with few students awarded As, most gaining Cs and Ds and a tail of lower achievers given Es and below. In 1992, 20.2 per cent failed the exam.

Until 1994, the most commonly awarded mark was a D. Then, from 1995 until 2003, the most frequently occurring grade was a C.

In recent years, the pattern has changed further, making the A-level unique among Britain’s mainstream exams. In 2004, for the first time, the most commonly awarded mark was a B. Now, for the first time substantially more A level entries were graded As than Bs. The bell-shaped curve has been replaced by a stepped line which descends from a relatively high proportion of students achieving A grades to the just over 3 per cent who failed this summer.

It seems likely that the structure of the curriculum 2000 exams, which allow students to find out mid-way through their courses how well they are doing and to resit those where their grades are low, is the reason for the changed distribution of A-level grades.

Relatively few GCSEs to date are modular and allow resits mid-course.

One exam expert explained that resits of the AS papers in particular gave students the chance to push their grades upwards. A good performance on one of these easier papers, possibly at the second attempt, can hide a relatively low mark on A2 exams.

Schools, he said, were also getting smarter about how resits could be used to improve an overall A-level grade, so were encouraging students to retake modules in the second year of the course.

Geoff Lucas, general secretary of the Headmasters and Headmistresses Council, said the fact that the AS now gives students a progress check on how they are doing mid-way through their courses means that those at risk of failing are more likely to drop out before the exams. This would cut the proportion of lower grades awarded. Those dropping out are not counted in the figures published last week; only those attempting the full A-level are.

Although many are keen to laud the hard work of students and teachers, Robert Coe, of Durham University’s school of education, said the changed distribution meant the grading system was not functioning properly.

“The grading system is no longer working at the top end. So many people are getting As, and three As in particular. That is not discriminating,” Dr Coe said.

One surprise this year for those who say that pupils now are going for “easier” subjects has been an increase in the number of candidates taking further maths. The subject, widely regarded as among the hardest, registered the second largest rise this year after critical thinking.

The Government is to respond to concerns about A-levels not discriminating enough at the top end by introducing an A* grade for courses finishing in 2010. It might be tempting to think that the grade distribution will simply shift upwards. However, A*s will only be awarded for performance on the tougher A2 papers, meaning that students will not be able to boost their overall grades with good performances on AS papers.

Last week, the Joint Council for Qualifications revealed that the proportion of students achieving A grades has risen more sharply in private and grammar schools than in comprehensives, colleges and secondary moderns over the past five years. However, the Government published alternative figures showing that comprehensives are now winning a far higher share of the total number of A grades awarded than they did in 1997.

The proportion achieved by comprehensive students rose from a quarter in 1997 to a third this summer. By contrast, the independent sector’s share fell from 33 to 30 per cent over the same period.

Leading article, page 16

‘Stop knocking students’, page 20