The concordat between local authorities and the Scottish Government was renewed yesterday, but the row over class sizes continued unabated.

The Herald revealed yesterday that a paper prepared by the councils' umbrella group Cosla recognised that "the pace of pursuit of class size reduction" would "vary from council to council" and that this could also vary from school to school within local authority areas.

This was seized on by opposition parties as fresh evidence that the SNP pledge to reduce class sizes in the first three years of primary to 18 was unravelling.

But an aide to the Education Secretary, Fiona Hyslop, insisted: "The paper presented to Cosla is a clear and unambiguous endorsement of the pledge to deliver year-on-year progress in reducing class sizes.

"With record low primary class sizes already being delivered, parents know that real progress is being made."

The leader of the SNP group on Cosla, Councillor Derek MacKay from Renfrewshire, welcomed the unanimous decision of the convention to renew the concordat with the Scottish Government.

He said local authorities also reaffirmed their commitment to work to reduce class sizes.

He said after the meeting: "The Convention today agreed to renew, refresh and refocus' our efforts with the Government on the outcomes agreed in the concordat.

"Cosla today recognised that we all need to do more to achieve lower class sizes and agreed that working together local authorities, Cosla and the Government will re-invigorate our efforts to cut class sizes in accordance with the concordat."

Labour's Shadow Education Minister Rhona Brankin said of The Herald revelations: "This shows clearly that the class-size pledge that was the major plank of the SNP manifesto is dead.

"Fiona Hyslop and her colleagues wrote a cheque to the Scottish people that they couldn't cash but rather than admit they got it wrong they instead attacked local authorities doing their best with the worst local government education settlement since devolution."

Tory education spokeswoman Liz Smith said: "The first round of Single Outcome Agreements revealed the truth - 15 out of Scotland's 32 local authorities made no mention at all of class sizes.

"Already, Moray, Perth and Kinross and Glasgow City Councils said that their latest Single Outcome Agreements will not contain any mention of class sizes and Glasgow said it had not even been asked by the SNP Scottish Government to include this."