An official report has found that more than a third of Scottish schools are still in poor or bad condition and it could take 20 years to modernise them all.

Despite recent investment in the country's schools totalling almost £4bn, the report published jointly by Audit Scotland and the Accounts Commission on Thursday discovered that 36 per cent of schools in Scotland may need 15 to 20 years to make them fit-for-purpose.

The sum of £3.9bn that has been spent since 2000 on improving the schools stock in Scotland will increase to an expected £5.2bn by April, it has been announced.

On the progress made, John Baillie, chairman of the Accounts Commission, said: "Ten years ago many of Scotland's schools were in state of serious disrepair. Since then, 219 schools have been built and many others refurbished. Councils are working hard to improve how they manage their school estates."

Meanwhile, Robert Black, auditor general for Scotland, stated that: "The national strategy should be reviewed, using the better information that is 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, entitled 'Improving the school estate', detailed avenues of possible funding which included private finance initiatives and public private partnerships.

Speaking to BBC Radio's Good Morning Scotland, minister for schools Maureen Watt said: "We've inherited a problem of decades of under-investment, it's not a problem that's going to be solved overnight."

In terms of what the schools strategy aims to achieve, the report stated: "The Scottish government and councils should review the School Estate Strategy and set specific, measurable and meaningful targets to ensure that the aims of the strategy are clearly expressed and progress can be properly assessed.

"The strategy should contain an implementation plan, which sets out what has to be done, when and by whom."

"The Scottish government and councils should report progress using information collected at an agreed time and to an agreed standard," it added.