The Assembly government is bracing itself for a "disastrous" set of international assessment results that will show Welsh pupils have fallen further behind those in the rest of the UK, TES Cymru can reveal.
Educationalists have widely predicted that Wales will perform poorly when the Programme for International Student Assessment (Pisa) results are published on Tuesday.
But a number of sources close to the government have told TES Cymru that the results - which have already been shared with officials - are even worse than feared, with Wales dropping down the world rankings by up to five places in some categories. Maths performance is thought to be particularly poor.
One source said: "It's close to a catastrophe. Wales has slipped badly." Another said: "It's disastrous; much worse than anything we had expected."
It is understood that officials in the Department for Children, Education, Lifelong Learning and Skills (DCELLS) have been holding a series of crisis meetings over the last month to discuss how to respond to the report.
Another source said: "DCELLS officials are looking very glum indeed. They know the situation is grim."
Pisa, run by the Organisation for Economic Co-operation and Development, is an international standardised assessment for 15-year-olds.
Sixty-five countries took part in the 2009 programme, which tested pupils' ability in reading, maths, science and problem solving.
The last set of Pisa results, in 2007, came as an embarrassment to the Assembly government as Wales performed the worst of the UK nations. Globally, Wales did well on science but turned in below-average performances in reading and maths, comparable to eastern European countries such as Croatia and Azerbaijan.
The government used the results as a catalyst to improve standards, including pioneering new developments such as the school effectiveness framework.
Education minister Leighton Andrews is expected to use next week's findings to reinforce the importance of the framework and to justify his approach to local authorities. He may also use them as an opportunity for tough talk with the teaching profession and to introduce new measures to hold schools to account.
Rex Phillips, Wales organiser of the NASUWT, said the results should not be used as a "stick to beat teachers with". "The minister should avoid knee-jerk reactions and work with the teaching profession, not against it," he said. "The results must be put in the context of the funding gap between Wales and England."
David Egan, professor of education at the University of Wales Institute Cardiff, said that the Pisa finding must be taken seriously by government, whatever the results.
Professor Egan, who was special adviser to former education minister Jane Davidson when Wales first took part in the Pisa system in 2006, said: "Are we optimistic that there are things in place that can help us get better results next time?"
Last month a Bristol University study found evidence that educational standards in Wales had slipped since league tables had been scrapped.
In a curt response, Mr Andrews said the government had implemented many of the changes wanted by the profession over the past decade, and the Pisa results would show whether this had paid off.
An Assembly government spokesman said: "The Pisa results are strictly confidential until released - we therefore have no comment."