Out of 2,606 primary and secondary schools surveyed, 479 were adjudged to be “poor”, or showing “major defects and/or not operating adequately”.
A further 31 schools were adjudged to be “bad” – where the building’s “economic life has expired and/or is at risk of failure”
The 19.5 per cent of schools in this category was marginally better than the previous year, when 20.5 per cent schools were deemed to be failing.
The figures in the report reveal that the number of schools either built anew or refurbished has halved over the last year.
Only 56 schools were either rebuilt or refurbished in 2010-11.
This marked a fall from 103 projects in 2009-10, 106 in 2008-9 and 93 in 2007-08.
The drop was largely because of a steep decline in the number of projects using private capital to pay for upgrades.
While 52 such builds took place in both primary and secondary schools in 2009-10, just nine were commissioned in the last year.
SNP ministers have plans to embark on a new school building plan.
But Labour claimed last night that the pipeline for new schools had now “virtually dried up”.
The figures showed that of the school buildings in Scotland some 1,558 were classed as “satisfactory”, where they are deemed to be “performing adequately but showing minor deterioration”.
A further 538 were recorded as “good” – or “performing well and operating adequately”.
The figures also showed that the number of school buildings registered either as “poor” or “bad” has fallen markedly from 993 five years ago, to 510 in 2011.
Education secretary Mike Russell said: “Key investment in school buildings have resulted in more children attending better quality schools.
“In the face of further Westminster cuts, we will continue to work hard to deliver further improvement.”
A Labour spokesperson said: “Cancelling Labour’s school building programme in the good years was a major mistake back in 2007, and five years on we see the consequences.”
He added: “Building schools isn’t just good for families – it’s good for the crucial constriction sector.
“Labour built and refurbished over 250 schools when in government and it is a tragedy that the SNP does not seem to share that ambition for our pupils.”