Advanced higher courses have defied predictions with a record number of entries in 2009.
The figures, which show a surge of interest in maths and the sciences, are a surprise boost to education leaders. Many predicted cutbacks would force schools to abandon them because of the small classes involved.
But some fear a two-tier provision is developing, and say the rise in uptake over the last three years has been inflated by the independent sector's embrace of the Advanced Higher.
There were 19,645 entries this year, up from last year's record of 18,854. This represents a 10 per cent jump in the two years of economic downturn since 2007, when the Headteachers' Association of Scotland (now School Leaders Scotland) expressed concern that schools did not have the resources to offer Advanced Higher. In the same two-year period, Higher entries rose by only 4 per cent, to 167,635.
Pass rates in Advanced Higher have risen this year by 2 per cent, to 77.8 per cent, and in Highers by only 0.8 per cent, to 74.2 per cent.
Brian Cooklin, head of Stonelaw High, Rutherglen, said while his school offered about a dozen Advanced Highers, the overall situation was "patchy" across Scotland.
Much of the increased uptake has been in independent schools - a rise of 16 per cent since 2006, but only 6 per cent in local authority schools (both sectors saw a rise of 4 per cent between 2008 and 2009).
There was a risk of two-tier provision developing, Mr Cooklin warned. Stonelaw helped by taking sixth-year pupils from other schools for Advanced Higher courses, but colleagues were concerned that "magnet schools" such as his would start to attract pupils from further afield at an earlier age.
Mr Cooklin, a former president of School Leaders Scotland, believes increased uptake might be explained partly by schools thinking ahead to the importance of Advanced Highers to the new baccalaureates.
Maths is the most popular Advanced Higher, up 10 per cent to 3,027 this year. There were also big increases in physics (up 10 per cent to 1,550) and biology (up 7 per cent to 2,095).
Rhona Goss, principal teacher of Monifieth High's science faculty and former chair of the Association for Science Education Scotland, said the rise might be explained by growing confidence about project-based work in upper school, as the ideas of A Curriculum for Excellence took hold. Schools were also now less inclined to let pupils "coast or mark time" during sixth year.
A Scottish Government spokesperson said that, given its aim to build Scotland's reputation as a centre of research and technology, it was "especially encouraging" to see a big rise in Advanced Higher physics entries, which were only 40 fewer than for English.