Many school buildings in Wales are still in a poor state following "weaknesses" in the management of the investment programme, says a report.
The Auditor General for Wales said there was a long way to go before all of them were "fit for purpose".
However, Gillian Body said many pupils and teachers had benefited from a "much improved working environment".
The assembly government said it was "implementing the recommendations" and schools should have modern facilities.
The auditor general's report, based on an audit in 2008-09, looked at whether investment in school buildings had been managed "to best effect".
Ms Body said a lot of work has gone into trying to get the schools estate in Wales "up to scratch".
But she said there have been "weaknesses" in the management and evaluation of the capital investment programme for schools and many buildings are still in a poor state.
"Recent changes introduced by the assembly government provide a firmer foundation for the future - although it's too soon to evaluate their impact," Ms Body added.
The report said that for a number of local authorities, effective planning of investment had been hampered by a "lack of reliable information about the state of school buildings".
Planning was also held back by a "reluctance to take decisions on school rationalisation following falls in pupil numbers".
Inadequate investment in school buildings and poor maintenance, particularly in the 1980s and most of the 1990s, had left school buildings in poor repair, said the report.
While there were now new schools in most parts of Wales, few councils had a clear understanding of how they would "fund the necessary improvements to the remainder of their schools".
The assembly government set a target in 2003 for all schools to be "fit for purpose" by 2010 and committed to invest £560m between 2004-05 and 2007-08.
The report said the "fit for purpose" objective was only defined in broad terms, resulting in "uncertainty about the quality of school buildings that local authorities should aim to achieve".
However, the report said the assembly government's policy of improving school buildings, and the availability of grant funding, had "improved the working environment for large numbers of pupils and teachers across Wales".
The assembly government had also introduced changes which had the "potential" to remedy past weaknesses in the planning and management of capital spending in schools.
An assembly government spokesperson said: "We are already implementing the recommendations set out by the Wales Audit Office as demonstrated in the transitional capital funding announced, and implementation of the 21st Century schools programme.
"It's important that children and young people have the opportunity to learn in modern facilities suitable for a 21st Century curriculum.
"The minister has announced £144.8m in new capital projects which will make a real difference to schools across Wales."
The money will be used to build schools, improve facilities, meet Welsh-medium provision and develop purpose-built special education needs schools.
Three new secondary schools projects, in Bridgend, Cardiff and Penarth in the Vale of Glamorgan, will be funded.