Wales braced for new Pisa education rankings
Wales will learn how its education ranks alongside other nations as the Pisa international league tables are revealed later.
Ministers warn the results could once again be disappointing, previously ranking Wales in the thirties and forties and the worst UK nation.
Half a million 15 year olds in around 70 countries are tested on maths, science and reading.
Opposition parties say the rankings will be a test of Labour's record.
When the last set of results came out in 2010, they were described as alarming by the then education minister Leighton Andrews.
In 2010, Wales was ranked 40th for maths, 38th for reading and 30th for science out of 67 countries that took part and was also ranked lowest of the UK nations.
Wales had slipped from the previous results in 2007 which were below the Pisa average and were far behind the rest of the UK.
In maths, for example, pupils in Wales were behind the UK average by the equivalent of six months of school.
'Far from inspiring'
The current education minister Huw Lewis has already warned people not to expect a major improvement.
He told BBC Wales in November: "I would not be surprised to see results which were, you know, far from inspiring."
The Welsh government has put a lot of emphasis on climbing international league tables and wants to be in the top 20 countries by the next round of tests in 2015.
Andreas Schleicher, deputy director of Pisa, told BBC Wales that would be difficult, but not impossible.
"It's a very significant challenge, but at the very same time if you look at the most rapidly improving education systems that pace of progress is really possible.
"If you think about Poland, or even bottom of the league table Brazil - one of the lowest performing countries - the pace of change we are seeing there is the one that would bring a place like Wales well into the top 20."
A number of changes were made to the education system in Wales following the disappointing results in 2010.
Children as young as seven are now tested every year and schools are put into bands as a guide to measure their performance. There is also a new framework, which teachers follow in the classroom.
Some schools like Bro Myrddin in Carmarthen have been using the Pisa technique and teachers there believe it helps pupils to think more independently.
But their enthusiasm for the system is not shared by everyone and some argue the tests themselves are flawed.
Professor David Reynolds, who advises the Welsh government on education, said opportunities were missed during the first decade of devolution in Wales.
He said: "Most other countries put in place functions, national programmes.
"England did it, most of Europe did it, to ensure that teachers had the best knowledge and approaches to be good teachers and help their kids, and we didn't. We thought, we're Wales - we don't have to do it."
David Evans, secretary of the NUT in Wales, said initial indications suggested there may be a drop in results.
"Pisa results are an interesting measure, but they're not the be all and end all when it comes to education here in Wales," he said.
"Yes, we need to measure ourselves against other countries, we need to see how we're doing, but we have our own curriculum here in Wales.
"We need to focus on what we want for our Welsh youngsters and take that forward."
But he admitted there were "issues" with education performance in Wales.
"We need to make sure the systems we've put in place in Wales have time to bite, have time to have influence upon our pupils and take it forward," he said.
"And obviously we need better resourcing in our schools and better opportunity for our youngsters in our schools."
Rex Phillips, Wales organiser of the teaching union, NASUWT, said the tests were never meant to define an education system, and said Pisa admitted that was not what they should have been used for.