The Auditor General for Wales said a lack of investment and poor levels of maintenance, particularly in the 1980s and 1990s, meant that many schools are still not up to scratch.
In 2003, the Assembly government set a target for all schools to be "fit for purpose" by 2010 and committed to invest pound;560 million between 200405 and 200708, and to maintain high levels of investment until the end of the decade.
But the report said the objective was only defined in broad terms, meaning local authorities were uncertain about the quality of school buildings they should be aiming to achieve.
Investment planning was also hampered by a lack of reliable information about the state of school buildings and a reluctance to take decisions to close schools with declining numbers of pupils, it said.
However, the report said the Assembly government's school improvement policy and the availability of grant funding had improved the working environment for many pupils and teachers.
Earlier this year, the phrase "fit for purpose" was officially jettisoned after it had been used to embarrass ministers and replaced with a 21st Century Schools standard.
Leighton Andrews, the education minister, this week announced pound;144.8 million of additional capital funding for schools on top of pound;289.6 million already announced in the past 18 months.
- Original headline: Buildings in disrepair despite improvement pledge, says report