A worldwide survey has revealed teenagers in Wales are falling behind other countries in basic education.
The 15-year-olds scored below average in maths and reading and average in science, said the Organisation for Economic Co-operation and Development.
The UK as a whole fared worse than in previous years, but Welsh students came bottom of the "home" nations.
The education minister welcomed the report as a "snapshot" of where Wales stands on the international stage.
The Programme for International Student Assessment (Pisa) performance tables are based on tests taken by 15-year-olds and involved 400,000 15-year-olds from 57 countries.
The results are published every three years, but the UK did not participate in the last round of tests, taken in 2003.
In what was the first year Wales has been considered separately from England, Welsh students fared significantly worse than their peers in their neighbouring country.
They tested below average in maths and reading, but average in science.
In maths, the mean score of students in England and Scotland was "significantly higher" than in Wales.
And while reading performance in England, Scotland and Northern Ireland was similar, in Wales the average score was lower.
Performance in science across all four parts of the UK was similar. But the report adds that the average score of students in Wales was significantly lower than in England.
Wales' Education Minister Jane Hutt reacted to the report saying her priority was to secure better outcomes for learners, not just to score highly in Pisa rankings.
However, she added: "Not that we do not recognise the importance of Pisa as a yardstick against which we can measure our progress.
'Strengths and weaknesses'
"The real benefits of the Pisa assessments will come not from the headline figures and league table rankings, but from the detailed analysis of strengths and weaknesses and what more we can learn from the best and most effective practice internationally."
David Reynolds, professor of education at Plymouth university described the survey results for Wales as "shocking".
"We are round about countries like Azerbaijan and Croatia and this should be some kind of joke but it is not," he said.
"There are two hints as to why this is happening. We don't seem to have enough able pupils.
"We always in Wales were told that our problem was the lower achieving pupils. But we have not got a high enough proportion of pupils doing well and so overall our scores are down.
"The other hint is that it is money. Over time the assembly probably has not spent on education what it should."
Prof Reynolds called for the creation of a cross party commission to investigate the findings.
Pisa researchers said they attempted to discover how well pupils could apply knowledge, rather than simply regurgitate facts and figures.
Their results marked a sharp fall for Britain overall from where it stood in 2000.
It fell from eighth to 24th for maths, with some pupils in China scoring top marks in the subject.
In reading, the UK fell from seventh to 17th, placing it below countries including Estonia and Poland.