But there has been no "stampede" to take advantage, according to Charles McAteer, headteacher of Dumfries Academy. "The evidence from research seems to be that mixed-ability classes raise the average level of achievement rather than depress it," Mr McAteer observes.
"Setting might advantage the top ability levels but it depresses attainment for the middle and lower ability groups."
This conclusion was endorsed by Professor Lindsay Paterson of Moray House Institute during his address to the secondary heads' annual conference in St Andrews recently.
Arguments against mixed-ability teaching have largely focused on the challenge it poses to teachers in coping with wide ranges of ability in a single class. Raymond Robertson, the Education Minister, called it "teaching to the lowest common denominator" in an attempt to reach the "mythical average pupil" when he addressed the Scottish Conservatives' annual conference in May.
Mr McAteer said there were practical objections to alternative approaches. It was also expensive to increase the number of teaching groups. "The fundamental problem with setting is that the timetable does not lend itself to setting in all subjects. Apart perhaps from the big departments of English and maths, you just cannot get the whole of a year group or even half a year group along to a department at one time.
"My fear is that, because there are these difficulties, pressure could arise for streaming pupils just for simplicity's sake. You could visualise the use of national tests for this purpose with, say, all the level E youngsters trooping together into the same class for all their subjects."
Mr McAteer said it was in the spirit of devolved management that heads had some discretion over the best way of delivering the curriculum. He was backed by Christine Dignan, Dumfries and Galloway's head of secondary education.
Ironically, the change in the council's approach, which was approved by the education committee in June, was prompted because some schools were flouting the 13-year-old policy of a mixed-ability, common course in the first two years. Instead of confirming the policy, officials recommended discretion in S2 and councillors insisted this should be extended to S1.
Education officials acknowledged the argument that differentiating teaching approaches and materials to take account of pupils with varying abilities "is difficult to manage and places heavy demands upon the class teacher". A move towards setting would also allow learning support to be concentrated where it is most needed instead of being "stretched thinly" across the first two secondary years.
The Dumfries and Galloway report said research evidence did not favour a particular approach. But Professor Adam Gamoran, an educational researcher at Wisconsin University who has examined evidence from both Scotland and the United States, said recently that abler classes were often allocated to more experienced teachers who interacted more with their pupils and had higher expectations of them (TESS, August 9).
The result, Professor Gamoran told a seminar in Edinburgh, is "polarisation with top students becoming more responsive whereas the less able were turned off". Streaming was more damaging than setting, he added, because matching abilities across a range of subjects was less exact than for a single subject.
Professor Gamoran warned that it would be "a mistake to mandate all schools" to follow a particular type of class organisation. Like Mr McAteer, he wants schools to be left to decide for themselves.
What the report recommends
* Education authorities should create conditions in which schools can operate the best forms of organisation for their own circumstances. Through quality assurance mechanisms, they should evaluate the outcomes of schools' performance at the upper primary and lower secondary stages.
* Promoted staff, especially headteachers, should take a more active role in class organisation. Their role should not be restricted to timetabling and establishing resource mechanisms, but should include class organisation within the agreed school policy on effective teaching and learning. The effectiveness of class organisation will be an important area for evaluation within overall monitoring of teaching and learning.
* All teachers will wish to consider the effects of the way pupils are grouped for teaching. This will include an open and honest review of organisation and time management in class, and of teaching style. Teachers should work with senior managers to evaluate school policy.
* Guidance systems should give higher priority to encouraging and monitoring all pupils' progress and achievement. Guidance staff need to make more use of prior attainment information and to pass relevant information to all staff, consulting with learning support teachers as appropriate. Contacts with primaries should begin earlier in the session.
* Learning support should not be affected by more flexible forms of class organisation. Targeting it for specific purposes should be made easier and more cost effective. In primary schools, the increased use of attainment groups beyond English language and mathematics should result in increased involvement of learning support teachers.
* Parents will need to be informed about the rationale behind a school's class organisation policy and be prepared to discuss with the school its effects on their child.
* Pupils should find that attainment groups and sets should make self-assessment and the setting of targets for improvement more manageable.