Scotland is among the worst countries in Europe when it comes to class sizes, says Jim Docherty, assistant general secretary of the Scottish Secondary Teachers Association. "Did you know, we are actually behind Romania?"
If that suggests a dubious state of affairs in the secondary sector, primary schools would seem to be faring no better according to Kay Hall, president of the Association of Head Teachers in Scotland which represents primary heads.
"Certainly, classes of 18 to 20 are not unusual in European primaries. We are way above their average and European colleagues are often quite shocked at our numbers," she says.
Class size is likely to be a key domestic issue in the run-up to the local and Scottish Parliament elections in May, with Labour and the Scottish National Party focusing on this issue.
In response to the national debate on education, Labour says it will "bring forward proposals to reduce class sizes and improve pupil:teacher ratios at critical stages, such as P7, S1 and S2, particularly in English and maths, and have more learning in small groups. We must make sure that pupils will benefit from falling school rolls over the next decade."
Most teachers generally welcome the idea of smaller classes and the size most commonly suggested in both sectors is 25 pupils. But not all practitioners are agreed about targeting certain classes.
Ms Hall, who is headteacher of West Kilbride Primary in North Ayrshire as well as the AHTS president, says: "The proposed situation of capping P7 to 30 pupils is quite bizarre. It means that the extra pupils you can admit in P4 - P1-P3 is capped at 30 - you then have to lose for P7.
"It's a complex situation as it is, without making it more complicated.
"If you are going to cap classes you should cap them all. Why miss out P4-P6?
"They say that in P1-P3 you learn to read and in P4-plus you read to learn.
In other words, by P4 you start to get a change of pace in individual learning and in maturity levels, so by P7 you can have levels A to E in one class.
"Every year group has essential learning. Education is continuous.
Therefore, you need continuity in class sizes throughout primary, not a change in P4 and change again in P7," she says.
The more radical proposal comes from the SNP, which wants to introduce a phased reduction of P1-P3 class sizes to 18 or fewer pupils, initially targeting areas of social deprivation.
"We've costed it at pound;120 million-pound;140 million plus teacher training costs of around pound;3.5 million per annum. This is a seven-year target," says Michael Russell, the Shadow Education Minister.
"I've no idea exactly how long it would take to reduce every class in Scotland to 18 or less but we're certainly looking at a generation.
"I think it's the biggest single investment we could make in education.
It's at the centre of our election pledges."
People are sceptical about such a plan, not least because of the financial implications in terms of the numbers of teachers and classroom accommodation required. Where is the evidence that smaller classes mean a better standard of education or higher attainment?
The SNP's policy on schools states: "A range of studies shows that children benefit most not just from a general reduction in class sizes but also from specific class sizes," without naming the studies or specifying the sizes.
Mr Russell says the SNP is following the Tennessee STAR model, arguing: "If they can reduce class sizes like this in Tennessee, why can't we do it?"
The STAR project was a large-scale experimental investigation of the effects of reducing class size in kindergarten classes (five-year-olds) and the first three years of elementary school. The only independent Scottish report on this project was commissioned by the Educational Institute of Scotland, which has never based any campaign for smaller classes on it or the 1996 Evaluation of the Tennessee STAR Research by Lindsay Paterson of Edinburgh University's education faculty.
Among his findings, Professor Paterson noted:l although the study found unambiguous evidence of an effect of small classes on achievement, that effect was quite small compared to the effects of other feasible interventions;l the moderate effect of reducing class size might not matter if this intervention did not cost much, but it does;l the benefit of being in a small class was evident quickly and did not grow even though pupils remained in a small class. So, whatever the arguments for reducing class size, they apply most strongly only to the very early years of schooling.
Professor Paterson concluded: "The educational significance of the findings is in some doubt, however. The size of the effect associated with reducing class size is small compared with other educational interventions, some of which would cost less."
Nevertheless, the perceived need for smaller classes is widespread. Pamela Munn, who led the analysis by Edinburgh University of views expressed to the Scottish Executive in the national education debate, says: "The desire for smaller classes was very prominent. It was one of the dominant themes from parents, pupils and teachers.
"While it's quite hard to get convincing research evidence of long-term benefits of class size, anyone who has taught knows that smaller classes are more pleasant for both teachers and pupils and it does allow you to get to know your pupils better."
Judith Gillespie, development manager of the Scottish Parent Teacher Council, believes that classes can be too small, however. "It is easy for a child to become isolated," she says.
"Take a class of 18, for example, with nine boys and nine girls who tend to play separately according to gender. A powerful personality in either group could attract six or seven and isolate the others. Or, if eight boys play football together, what happens to the other one?
"School is often the child's social context. So if they're not enjoying the social side, they won't enjoy school and they won't learn, or at least won't learn as well as they could."
Mrs Gillespie does not believe class sizes of 18 are feasible in most school buildings as they are; and there is no evidence of public-private partnership schools being designed with this in mind.
"We have to allow schools flexibility to adjust class sizes to suit circumstances. This would involve protecting them against placing requests," she says.
"The system at the moment does not generally allow schools to reduce class sizes. It destroys the flexibility."
The SSTA fears that, rather than getting smaller, classes could actually go up in size.
"All this talk of reducing class sizes is just political speak. It's spin," says Mr Docherty. The reality is something different.
"Post-McCrone, the restructuring in most local authorities, as far as I can see, is going to involve a reduction in the number of principal teachers and the creation of a new breed of super or faculty PTs who may be entirely non-teaching or on a half timetable. The only mechanism to allow for this will be to increase class sizes.
"Add to this the fact that a probationer is now promised a 0.7 timetable.
Who covers the other 0.3? Another instance for increasing class sizes?
"The SSTA believes that early retirement packages may be being considered for PTs who don't want the super posts. How will their retirement be covered? By increasing class sizes?"
In spite of a lack of proven long-term advantages, there seems to be a general desire in Scotland for smaller class sizes and many consider the issue too important and too complex to be left to politicians.
LET'S DOWN-SIZE WITHOUT DOGMA
Brian Boyd, senior lecturer in education
"A recent study by Peter Blatchford at the Institute of Education, London University, supports US research that class size reduction can have a positive impact on attainment. But the reduction has to be dramatic, halving our present classes to 17 or 18.
"I think our long-term aim should be to have classes of around 20 in both primary and secondary schools. I think it's achievable in the long term if accompanied by teacher training and continuing professional development in methodologies, including team teaching, co-operative learning, looking at individual learning styles and so on.
"We'd need to employ more teachers and more classroom assistants and this is where we need to go first.
"The biggest single problem is accommodation. We need to look to the long term and build for the future."
Moira Leslie, headteacher
Raigmore Primary, Inverness
"Thirty three children in a class is too much at any stage and the drop to 30 has certainly helped - coupled with the input of classroom assistants - in the early years.
"My staff would be against classes of 18. As we have a lot of army children here, we are used to sudden drops to small classes when regiments leave. The social mix changes; there isn't the same spread of role models in class. Good discussions and good circle time can be hard to achieve. There's less opportunity for friendship groups and interest groups among the pupils. The sparkle goes.
"For lower primary, maybe 20 would be fine, but for upper and middle school, 23-25 (and I mean 25 max) would be optimum.
"There's a great difference between 33 and 25 and 25 would help greatly space wise, planning wise and for teaching and learning in general."
Judith McClure, headteacher
St George's School for Girls, Edinburgh
"Class size is very much an issue for parents placing their children in the independent sector. Our maximum is 24 for core subjects. Our maximum in P1 is 20.
"It's a challenge to both public and independent sectors because you have to balance cost against size.
"I think reducing class size should be a matter of policy, not simply a by-product of demographics. I don't think it's about numbers like 18 or 25.
It's about learning and teaching methods, about being imaginative about the buildings, the environment, the subject, the facilities and the approach.
"You could argue you need 20 pupils for social cohesion, but different sizes suit different subjects and different stages. There's always the place for both an auditorium presentation and a small study group.
"I have never seen any research which proves that smaller classes raises attainment, but ask any teacher and they'll say a smaller class - but maybe not too small - will impact on attainment."
Frank Lennon, headteacher
St Modan's High, Stirling
"I think the Labour position on reducing class sizes and improving pupil:teacher ratios in S1 and S2 is consistent with the provision of comprehensive education for all, unless this is a code for rigid setting or streaming.
"We need to bring maximum sizes down from 33 to around 25, especially for core subjects. But I'm against dogmatically imposed norms per se and I don't think 18 is realistic. There would be enormous accommodation issues.
"I don't believe there is an ideal class size: the most successful schools are often packed to the gunwales. It's how we define mainstream experience that is critical.
"I'd rather have smaller mainstream classes than extraction units. The proliferation of specialisms to cope with whatever problems a pupil may have is mind-boggling.
"The debate really revolves around the provision of more and more fragmented support like this or having smaller mainstream classes."
Roy Henderson, principal teacher of English
Leith Academy, Edinburgh
"On paper we have a 33 limit but in S1 30 is the reality and it drops to the high and mid-20s by S3-S4.
"Social inclusion has rendered these sizes more difficult and smaller classes are necessary. On their own, smaller classes will not solve the social inclusion problem but it would help both the social inclusion and other pupils.
"We also need a new, mature and sophisticated series of structures involving more specialist and support staff, in both classrooms and bases outwith, to neutralise the effect social inclusion pupils have on classes as a whole.
"Given the nature of our catchment area - a deprived city centre - social inclusion tilts us towards the desperate.
"Classroom assistants cannot be counted towards reducing the adult:pupil ratio in secondaries because we do not employ them in the classroom. They are more like subject auxiliaries or staffbase factotums."
Chris Sugden, headteacher
Buckie High, Moray
"If you really want to affect the pace of learning in S1 and S2 it's imperative to bring class sizes down to around 20.
"We could accommodate these classes in the present school buildings with a handful of extra staff. Very few schools operate at 100 per cent capacity.
"Reducing class size is so important in the push to raise literacy and numeracy and it's almost impossible to teach core subjects and modern languages in classes of 30-plus.
"Classes of 20 would be a matter of timetabling. It would actually make timetabling easier if you had one class size and it would make the tracking of pupils easier.
"I think size is a big issue, especially in S1 and S2. It's crucial to tackle it to raise attainment."