Wales awaits Pisa education rankings outcome
Wales will find out how its education system compares to other countries in the world when the latest Pisa results are published on Tuesday.
The tests look at reading, writing, maths and science abilities of 500,000 15-year-olds from around 70 countries.
In 2010, Wales was 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 countries.
It is expected to have slipped down the table again this year.
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, agrees that will be difficult, but not impossible.
He said: "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."
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.