The report, Improving the school estate, warns that about one third of schools are reported to be still in poor condition and it is estimated that at current rates it will take another 20 years to make all schools fit for purpose.

Since 2000, £3.9bn has been committed by the Government and councils to improving Scotland’s school estate, and this is expected to increase to over £5.2bn by April 2008.

Audit Scotland said that the Government and councils now need to draw up detailed plans to make sure that all the remaining schools are fit for 21st century education.

An early problem was that environmental sustainability was not a key factor in the designs, but more recently there have been some good examples of environmental factors being considered, said the spending watchdog.

Accounts Commission chair John Baillie said: "Ten years ago many of Scotland’s schools were in a state of serious disrepair. Since then 219 new schools have been built and many others refurbished. Councils are working hard to improve how they manage their school estates. They need carefully to devise their financial strategies, paying particular attention to future costs and to ensuring that they are able to adapt to changing needs such as pupil numbers, curriculum changes and community needs.

"Councils could also do more to share good practice and improve designs, and make environmental sustainability a key consideration."

The school estate strategy launched in 2003 was criticised for a lack of clear definitions, and resulting difficulties in measuring how many schools have been improved.

Robert Black, Auditor General for Scotland, said: "The national school estate strategy gradually evolved, with the guidance being developed after the building programmes had started. The strategy did not set out exactly what needed to be done nor how it would be achieved. The national strategy should be reviewed, using the better information that is now available to specify the performance targets of the programme. Particular attention needs to be paid to future costs and how the remaining improvements will be financed."

The report sets out a number of further recommendations for the Scottish Government and councils and will be considered at the Scottish Parliament’s audit committee on 26 March.