Ms Hyslop has denied backtracking over class sizes
Education Secretary Fiona Hyslop has told MSPs the recession has slowed progress on cutting class sizes.
In the run-up to the 2007 Holyrood elections, the SNP said it would cap pupil numbers at 18 in the first three years of primary education.
In September, Ms Hyslop said she would bring in legislation to cap numbers at 25 pupils and only in primary one.
During Holyrood's education committee, opposition MSPs accused the minister of dumping manifesto promises.
Committee convener, Labour MSP Karen Whitefield, said the pledge was in tatters and would not be delivered in the lifetime of the current Scottish Parliament.
But Ms Hyslop said she did not expect councils to deliver the target in the current economic downturn, telling MSPs: "Do I want progress to be quicker? Yes I do, but I recognise some of the pressures that local government faces.
"I think it would be unrealistic at a time of recession not to recognise that what we wanted to achieve in our manifesto in 2007 when you're sitting in a period on 2009 and we see the real pressures, not just on public services, but across the country."
Following the committee meeting, Ms Hyslop announced that the president of the Association of Directors of Education Scotland, David Cameron, will lead a review of mechanisms for controlling class sizes.
Measures such as regulations and teachers' terms and conditions can be used to control how many pupils are in each class.
Having a "coherent approach will help local authorities and government to ensure more effective educational provision for Scotland's young people", Ms Hyslop said.
The education secretary's comments came as Eric Wilkinson, professor of education at Glasgow University, claimed the Scottish system had become parochial and stagnant over the past decade, and called on political leaders to embrace new ideas.
His claim was dismissed by the primary head teachers' union, AHDS, which said the new curriculum encouraged pupils to think for themselves and be adaptable, rather than being spoon-fed knowledge.