Wales's education system has been overhauled in the wake of its "disastrous" performance in the 2009 Pisa (Programme for International Student Assessment) rankings. Back then, the results showed that the country's 15-year-olds had performed worse than their peers in the rest of the UK in reading, maths and science.
But despite a raft of reforms, senior figures including education minister Leighton Andrews have cast doubt on Wales's ability to improve its standing in international education tests.
Speaking at a major conference on Pisa last week, Mr Andrews admitted publicly for the first time that Wales may not improve its international score when the country's 15-year-olds sit the next set of tests in the autumn.
"As the next assessments approach, my officials are focusing on strategies to improve the weaknesses identified in Pisa," Mr Andrews said. "I know my ambition for Wales to climb the Pisa rankings is a significant challenge, and it would be unrealistic to expect significant improvements in the 2012 results.
"Systemic change takes time if it is to have a lasting impact. Experience tells us that quick fixes are seldom sustainable."
Mr Andrews' comments come despite previous statements that his aim was for Wales to become a top 20 Pisa country in the 2015 round of tests. Wales ranked 30th out of 67 countries for science in 2009, compared with 38th for reading and 40th for maths.
A senior figure from Pisa, which is run by the Organisation for Economic Cooperation and Development (OECD), also suggested that the top 20 aim may be too ambitious.
"A 20-point increase in the space of six years would be a challenge," said Pisa's senior analyst Michael Davidson. "It's not impossible, but it would be at the upper end of what other countries have achieved. It's a stretching target, but then that's what targets should be."
Mr Davidson said that Wales's pupils were a full two school years behind their counterparts in leading Pisa regions such as Shanghai, and half a year behind the OECD average. However, he added that certain countries had made great strides in the past, including Chile, which improved its Pisa score by 40 points in a decade.
He said that it would be wrong to concentrate solely on climbing the Pisa league table, and that focusing on improving the skills that the tests measure was more important. He dismissed critics of Wales's focus on international rankings, who have accused Mr Andrews of an "obsession" with Pisa.
"Pisa is an external mirror for education systems around the world to look at themselves and each other," Mr Davidson said. "If you value the skills it is measuring then it is not wrong to view Pisa as a benchmark or an aspiration to improve."
Mr Davidson also said that one of the main issues with pupils in Wales is that they do not enjoy reading outside school. The difference between those pupils and their counterparts who read for up to 30 minutes a day can be as much as 50 score points on the Pisa scale.
Professor David Reynolds, a senior adviser to the Welsh government, said he would be surprised if there was any increase in Wales's Pisa performance this year.
"Given that the focus this year is on maths, in which we had a rapid decline in results between the 2006 and 2009 tests, I'm not optimistic about our chances," he said. "But the focus in 2015 is on science and because of that we can do a whole lot better than people might think. We are already starting from a pretty strong base in science and we have another three years to get it right."
When the last results were published in 2010, Mr Andrews described them as a "wake-up call to a complacent system" and said there had been a failure of leadership at all levels. The results were described by one senior government figure as "disastrous".
Mr Andrews launched a 20-point action plan to improve standards, which has already seen the formation of a school standards unit to improve accountability, the introduction of secondary school performance banding, and the launch of a literacy and numeracy framework.
The Conservative opposition in the National Assembly has accused the government of "washing its hands" of the current cohort of teenagers while it works out how to perform better in 2015.
'Get a grip'
Education secretary Leighton Andrews has urged local authorities to "get a grip" on their responsibilities.
In the wake of the 2009 Pisa results, he warned Wales's 22 councils that they must improve rapidly or face radical restructuring.
Speaking last week, he said: "Local authorities have to demonstrate that they are both delivering improved performance and delegating 80 per cent of their budgets to schools by September 2012 and 85 per cent by September 2014."
Mr Andrews added that they have to show they are "getting a grip" on services to support headteachers and school organisation issues, including catchment areas and Welsh-language education.