A-level grading system is a lottery, says exams expert

A strong warning that A-level grades are unreliable is delivered by one of the country's foremost experts on assessment today - just 48 hours before 250,000 students receive their results.

A strong warning that A-level grades are unreliable is delivered by one of the country's foremost experts on assessment today - just 48 hours before 250,000 students receive their results.

Someone awarded a B grade could just as easily have been given an A or a C, according to a report compiled by Professor Roger Murphy, professor of education at Nottingham University and a former president of the British Educational Research Association.

He is an acknowledged expert on assessment who has worked for both the Government and its exams watchdog.

Professor Murphy argues that the award of any grade is only a compromise - and can depend on the mood of the candidate, which teacher marks their script and which of the three main exam boards has set the paper. "There is a risk of giving examination grades unwarranted significance in forming judgements about individuals or about the success of teachers, schools or education institutions," he says.

Students' marks could vary depending upon which day they sat their exam. "We all have good days and bad days and one-off examinations have no way of accommodating for that," he says.

Markers can also make "human judgemental errors" so that one teacher could award a different grade to another.

"Public examination grades are approximate," he says. "They depend upon the judgement of fallible human beings. They depend upon snapshots of student performance under certain conditions, at a certain point in time, in response to a certain set assessment tasks."

One way to produce more dependable grades, he says, is to have a large number of examiners assess each student - and reach an average grade.

An alternative would be for the student to sit the exam in a variety of different conditions.

The report, commissioned by the Association of Teachers and Lecturers (ATL), also argues that the existence of five different examination boards - three in England, one for Wales and another for Northern Ireland - is a further source of uncertainty. "Do all of these awarding bodies set different types of examinations and operate with different grading standards, people might wonder?" it asks. But it warns against a move towards a national examination body on the grounds that it would be more susceptible to government interference.

Professor Murphy also cautions against comparing standards over time. "If we tried to apply 1984 grading standards in 2004 it would be a complete nonsense," he says. "The curriculum necessarily has to move with the time and public examinations are designed to reflect the nature of that curriculum."

Gwen Evans, deputy general secretary of ATL, said: "As we near the annual exam results frenzy, parents, learners and teachers alike need to be aware of the element of chance inherent in even the best-run assessment system."

Headteachers are opposing a plan to split A-level A grades into four. The plan by Mike Tomlinson, the former chief schools inspector, is aimed at helping university admissions staff select the brightest candidates, now that one in five scripts are awarded an A grade. David Hart, general secretary of the National Association of Head Teachers, said: "To send the message that the A-grades achieved by this year's students are not somehow worthy of recognition across the board would be damaging to the morale of the pupils and their teachers."