The survey which gathered information from 22 out of the 32 local authorities in Scotland found that lowering class sizes to 18 pupils in P1-3 would cost an extra £62m every year and require an additional 2,173 teaching staff. An extra 900 classrooms would also be necessary at a cost of £360m according to the ADES report.

The strategy to achieve the 18 pupil limit target by 2011, according to the ADES, could include redrawing catchment areas, a phased progression towards the target, school extensions and temporary accommodation, extensions to schools and temporary accommodation and allocation of two teachers to large classes.

The SNP Government has allocated an extra £40m to local authorities to support them in implementing the flagship class size policy.

Responding to the claims from ADES a Scottish Government spokesman said:

"The local government settlement specifically included a special provision to maintain teacher numbers nationally at 53,000 in the face of falling school rolls - by doing this local authorities can reduce class sizes.

"Recurrent local government budgets are increasing by 5 per cent, 4.1 per cent and 3.4 per cent over the next three years.

"We expect year-on-year reductions from local government as a whole, and by each local authority over the spending review period."

Liz Smith MSP, Conservative Shadow Minister for Children, Schools & Skills, said:

"This just proves what many of us have been saying all along. The SNP initially told us that an additional £40 million would be set aside for local authorities to pursue the policy of class sizes of 18 pupils in primaries one to three. The ADES survey tells us it is more likely to be £422 million, given that £62 million will be needed for additional staff and £360 million for new classrooms. It proves Fiona Hyslop can't count and it also proves that the class size policy in P1-3 is simply not sustainable with the limited resources available. The Scottish Government has made a huge miscalculation and should apologise unreservedly to all parents, pupils and teachers for raising expectations to a level which they will never be able to fulfil.

"It is also interesting to note that ADES does not believe a one-size fits-all reduction in class sizes is wholly appropriate when it comes to driving up educational standards within the first three years. This is correct. Deciding on class sizes or what is best for individual pupils in individual schools should be a matter for the headteacher, not the Scottish Government or a local authority, and I know that there are many teachers and parents all across Scotland who agree.

“Effective learning is, first and foremost, about good teaching in a calm and disciplined environment and so there are many circumstances where parents would opt to have their child taught in a slightly bigger class if it means better teaching, better discipline and better access to a better school. There is, by no means, always a direct correlation between lower class sizes and better attainment. Therefore the Cabinet Secretary must now accept that she has made a serious error of judgment – to say nothing of her seriously flawed arithmetic.”

Murdo Maciver from ADES gave evidence on the matter before the Scottish Parliament's Education, Lifelong Learning and Culture Committee at Holyrood today.

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