Data from the Scottish Qualifications Authority reveals a common trend for pupils to "waste time" sitting the Intermediate 2 version of a subject - even though they have taken the same subject at Standard grade.
"This is an elephant in the room," said Mark Priestley of Stirling University. "Everyone knows it goes on, but prevailing school culture doesn't allow alternatives."
Dr Priestley discovered that, of 24,444 Standard grade English Credit passes in 2008, some 5,576 passed Intermediate 2 the following year (or 23.5 per cent of all Standard grade Credit candidates).
He also found significant proportions of 2008 Standard grade candidates in other subjects who went on to do Intermediate 2 after achieving a grade 1 or 2: notably PE (12 per cent); maths (7.9 per cent) and biology (7.1 per cent). The overall figure is 8 per cent.
"We should question the rather dubious practice of requiring pupils to waste a year sitting duplicate qualifications," Dr Priestley said.
He believes the practice can be largely explained by the pressure on schools to raise attainment and avoid slipping down unofficial league tables, by pulling pupils out of Higher courses when they are struggling and placing them in Intermediate 2 classes.
He also blames "poor understanding" of the Scottish Credit and Qualifications Framework, which puts both Intermediate 2 and Standard grade Credit at Level 5. "It may be that poor advice about progression simply reflects a lack of understanding of the equivalence of the two qualifications," he said.
Dr Priestley conceded that Intermediate 2 might be a better preparation for Higher, but that this was an argument for replacing Standard grade in S3 and S4, "rather than simply using it as a fallback position in S5".
He dismissed arguments he had heard from some schools that, since Intermediate 2 was more highly valued by universities, the practice was justified. Glasgow and Edinburgh universities, in fact, had told him it was "detrimental to the admissions prospects of young people, since it reduces breadth".
He added that some schools' decision to introduce early presentation was "exacerbating the problem", with English and maths compulsory for large numbers of pre-16 pupils who already have Standard grade. One alternative, he suggested, could be for pupils who drop a Higher to be given free time to focus on their other Highers.
Ken Cunningham, general secretary of School Leaders Scotland, said the sitting of Intermediate 2s after achieving a high pass mark at Standard grade was not ideal, but not as undesirable as it might first seem. At least pupils should get a qualification, whereas in the past they would have had to muddle through Higher, probably fail, then take the same Higher again in S6. He stressed, too, that Intermediate 2s did not cover the same ground as Standard grades.
Mr Cunningham believes the practice usually occurs with a pupil's best interests in mind, while conceding that a minority of schools probably are trying to massage Higher pass rates.
A spokeswoman for the Scottish Qualifications Authority said that similarities between content and assessment of Standard grades and Intermediates could vary widely across subjects. In some areas, Intermediate 2 was a good bridge to Higher since there was a close resemblance between the two levels in assessment and structure of learning. Some subjects, such as English, had a wide choice of content; a candidate could be learning about very different things in Intermediate 2 from Standard grade.
A spokesman for the Scottish Government said: "Standard grade and Intermediate qualifications were originally intended for different year groups with different structures and purposes. However, over the years these variations have become unnecessarily complex."