The number of pupils sitting Scotland's most prestigious qualification has dropped sharply since last year, prompting calls for an urgent review.

Official figures show that the number of Advanced Higher examinations sat in Scotland has declined from an all-time high of 18,258 in 2006 to 17,825 this year. While not all subjects at Advanced Higher are in decline, with English seeing an increase, numbers of candidates sitting mathematics, computing, physics and history have all seen a drop.

The Advanced Higher was established to give the brightest pupils in Scots schools a qualification in their final year which would prepare them for the rigours of university life and is seen as superior to A-levels by leading UK universities including Oxford and Cambridge.

However, the qualification is also seen as expensive to run by schools because it requires a teacher to give up several hours a week to teach just a handful of the brightest pupils.

Last year, Highland Council warned that schools may have to consider cutting Advanced Highers in order to meet the requirements of the 2001 McCrone deal on teachers' pay and conditions, which cut the amount of time teachers spend in the classroom.

Bruce Robertson, who was the local authority's director of education at the time, warned that decisions to reduce curriculum options such as Advanced Highers were being looked at by schools because the courses attracted "very small numbers of pupils".

The 2.4% drop in numbers taking the exam across Scotland, revealed in yesterday's figures from the Scottish Qualifications Authority (SQA), will fuel concern that schools cannot afford to deliver the courses.

David Eaglesham, general secretary of the Scottish Secondary Teachers' Association, said: "The SQA needs to find out as a matter of urgency why the numbers sitting Advanced Highers is in decline and whether it is an issue of resources.

"This is an important exam because it stretches those at the top of the scale in their chosen specialism and if pupils are being prevented from doing that then we need to know why."

A spokesman for the Educational Institute of Scotland said: "We have noted the decrease in presentations at the Advanced Higher levels and believe these examinations remain an important part of our examinations framework.

"While the reasons are difficult to gauge, it is vital that pupils retain a wide range of options so that they can study on programmes which are best-suited to them and which give the best chance of achieving success in their chosen subjects."

However, Judith Gillespie, policy development officer for the Scottish Parent Teacher Council, said part of the problem was persuading pupils who had already got into university that the Advanced Higher was worthwhile.

"Many youngsters don't understand the benefits of studying an Advanced Higher because they are pragmatic by nature and do what is required.

"Because this is not an absolute requirement, some schools may struggle to persuade pupils that this is worthwhile," she said.

A spokesman for the SQA said: "Advanced Higher is well-recognised in the academic world as a robust and worthwhile qualification. We are aware of this slight dip in numbers at Advanced Higher and we are investigating the reason that this has happened, including demographic changes."

Meanwhile, Glasgow City Council yesterday welcomed figures which showed attainment levels among pupils in the city were either broadly similar to last year or had improved. While Standard Grade results were the same as 2006, which was Glasgow's best-ever year, the Highers results achieved this year had improved.

Gordon Matheson, the council's executive member for education services, said: "We are intent on bringing about a sea change in the attainment and achievement of Glasgow pupils."