Results from the world's most respected international study of education to be published next week are expected to show that overall standards in England's schools have failed to improve significantly since 2006.
The Programme for International Student Assessment tests of 15-year-olds in 2009 will confirm that the UK has failed to regain the comparatively high positions it enjoyed in literacy, maths and science in 2000.
They will be seized on by Coalition politicians, who have cited previous Pisa results as evidence of declining educational standards under the Labour government. In fact, the OECD, which compiles Pisa, no longer views the UK's 2000 results as statistically valid. But they are also used in a major report on school improvement by consultants McKinsey this week.
Pisa has become increasingly important in influencing global education policy since it was introduced in 2000. The first results showed the UK was fourth in the world in science, seventh in reading and eighth in maths.
Professor David Reynolds from Plymouth University believes next week's report "won't be a good Pisa for England", but that it will continue to head the four home nations.
The TES understands the Welsh Assembly government is bracing itself for a "disastrous" set of results. The principality is expected to drop down the world rankings by up to five places in some categories, with maths performance thought to be particularly poor.
John Bangs, a special consultant to teaching unions on the OECD, said Pisa was now the "pre-eminent" international study. "Today it is central in any Government's evaluation of their education policy," he said. "I think it has had a healthy effect on policy-making because it looks at achievement right across the board."
The programme has grown in stature because it allows comparisons over time - more meaningful than the "snapshot" of a single survey.
The decline between 2000 and 2006, that saw the UK fall to 14th in the world for science, 17th in reading and 24th in maths, was noted by the coalition Government in last week's schools white paper. It stresses the need to "benchmark" the performance of pupils in England against the "best in the world", through studies such as Pisa.
But the UK will be missing from comparisons between 2000, 2003, 2006 and 2009 when the most recent results are published on Tuesday because not enough of its schools participated in the first two surveys.
The Government is understood to have seen the latest unpublished Pisa results for 2009 before the white paper was completed. It makes only one mention of Sweden, which partly inspired ministers' flagship "free schools" policy, suggesting that the country may have slipped in the rankings. However, Finland, which has a strong track record in Pisa, received nine mentions.
McKinsey report, page 7.