The exams watchdog is investigating persistent complaints from head teachers that this year's A-level results were "fixed" to stop grades ballooning.

As it is, in what was the first year of the new A2 exams, the overall pass rate shot up by 4.5 percentage points, to 94.3%.

But some have complained that coursework seems to have been marked very aggressively - with students who were getting A grades in exams being failed on their coursework.

Now, the Qualifications and Curriculum Authority (QCA) has confirmed that it is looking into the allegations.

This is further evidence there is no single gold standard of A-level

John Dunford Secondary Heads Association

It said statistical evidence about the distribution of grades between units was being examined and individual cases were being followed up.

"However, on the basis of our extensive observations of awarding meetings over the summer, we believe that the awarding process is sound."

It believes the overall A-level results were sound but is investigating details.

But the leader of the Secondary Heads Association, John Dunford, said there should be an inquiry.

"It was always going to be difficult for exam boards in the first year of a new system but it seems to me that these problems should have been ironed out at a much earlier stage if we are to have public confidence in A-level standards," he said.

"We already knew that some A-levels are easier than others and this is further evidence that there's no single gold standard of A-level, as ministers have pretended for many years."

How it works

The awarding meetings referred to by the QCA - involving senior examiners within each exam board - are where the boundaries between grades are determined.

A-levels are graded from A down to E, with U (unclassified) being a fail.

The QCA says the senior examiners use "a variety of evidence and their expert judgement" to decide what mark is needed to achieve a particular grade.

First they decide on a preliminary boundary.

Working down from the top, they decide on the lowest mark worthy of a particular grade.

Then working up from the bottom they decide the highest mark that is not worth that grade.

"They then decide where the final boundary mark should be using a range of evidence," the QCA says.

One of the most important bits of evidence is usually the previous year's grades.

The problem this year was that, because the system was new, there was no clear precedent.

Top student

The most persistent complaints about this year's results relate to psychology, English and history awards by the OCR exam board.

OCR's Ron McClone is to meet head teachers

OCR confirmed the number of requests for inquiries into grades had jumped from 1,600 last year to 4,000 but it insisted it had followed the rules.

The board's chief executive, Dr Ron McLone, is to meet leading private school heads next week to discuss their concerns.

The head of Dulwich College in London, Graham Able, said at least 30 independent schools had concerns about the way coursework had been graded, and he knew of some state schools which were also worried.

One of his former pupils, who had been offered places by both Oxford and Yale in the US, but had decided to go to Harvard, got a U-grade for history coursework that his teachers believed was way beyond A-Level standard.

New system

OCR said all its procedures conformed to the QCA's code of practice.

Schools had been warned that A2s, the second half of the new A-levels introduced in September 2002, were meant to be harder than AS-levels.

"It is, however, possible that those involved in teaching at AS-level may not have fully appreciated the significantly harder demands of A2 assessment, particularly in coursework."

This is the nub of the problem - the new "Curriculum 2000" system.

A-levels in England, Wales and Northern Ireland are now a two-stage process.

Students take AS-levels in their first year of post-16 study - both a qualification in their own right and the first part of an A-level.

Boom - in retakes?

If they choose to continue with a subject to A-level, they then take A2s in their second year.

The QCA says the AS-level is pitched below the level required for an old A-level, in recognition of the fact that students will have been pursuing the course for a shorter period of time.

The A2 is pitched at a higher level. The final A-level is a combination of the results from the two parts.

This year the number of AS-levels taken was up by a quarter on last year - because, it is thought, many students chose to re-sit the exam with a view to improving their overall A-level grade.