Pisa ranks Wales' education the worst in the UK
Wales has fallen behind the rest of the UK significantly in reading, maths and science for the third time, an international study has shown.
In Wales, there were lower results on average in the three subjects than in England, Northern Ireland and Scotland.
Scotland leads the way in the UK in maths and reading, while England is ahead in science.
- In maths, Wales fell three places to 43rd of the 65 countries
- In reading, the nation is now ranked at 41 down from 38
- The biggest fall came in science where Wales dropped six places to joint 36th
The figures, published by the Organisation for Economic Co-operation and Development (OECD), show that for maths, 15-year-olds in Wales scored 468 points on average, compared with 498 in Scotland, 495 in England and 487 in Northern Ireland.
In reading, Wales scored 480, but Scotland scored 506 points on average, England scored 500 and Northern Ireland 498.
In science, Wales scored 491, compared with England's average score of 516, Scotland's 513, and 507 in Northern Ireland.
The OECD report concluded, for each of the three subjects, "performance in Wales was lower than the rest of the United Kingdom".
It is the third time Pisa has conducted such tests.
Since 2007, Wales has slipped down the Pisa rankings. As more countries have joined, it has slumped from 22nd in science to joint 36th, dropped 10 places in maths and fallen from 29th in reading to 41st.
Speaking about this year's results, Education Minister Huw Lewis said the results were disappointing and showed Wales had a long way to go.
But he insisted the news reinforced the Welsh government's case for the ambitious reforms it has already developed.
"Everybody working in and around the Welsh education sector needs to take a long hard look in the mirror this week," he said.
"The Pisa results are stark and the message is very clear, we must improve educational attainment and standards right across the board."
Mr Lewis said new reading and numeracy tests, secondary school banding, extra funding for new schools would take time to have a "significant impact" in Wales.
"There are no quick fixes," he said.
"I expect to see the impact of our reforms reflected in the next set of results. They're ambitious and I believe they will have a lasting, sustainable and positive effect on education in Wales."
Welsh Secretary David Jones urged Welsh ministers to "address these serious educational deficiencies and give the young aspirational people of Wales the skills they need to succeed".
Angela Burns, Conservative shadow education minister in the assembly, said: "These truly appalling figures show Wales' educational performance has at best stagnated, and at worst declined, and that in educational terms, Labour ministers have wasted the past three years."
Welsh Liberal Democrats leader Kirsty Williams tweeted: "Really sad and angry that 14 years of Welsh Labour Education Policy has led us to these #PISA results."
Plaid Cymru's education spokesman Simon Thomas said the results were not good enough.
"Wales cannot progress unless we get the basics right and that means meeting the challenge of improved numeracy, literacy and skills for all," he said.
All the UK nations were beaten in all three subject areas by the Republic of Ireland, and by Finland, a country which many education experts in Wales have sought to learn from.
Meanwhile the business group CBI Wales said the results gave cause for concern.
Emma Watkins, CBI Wales director, said: "It's not acceptable for Wales to have slipped so far behind, and this should be a wake-up call to those who care about the future of the Welsh education system."
But Chris Keates, general secretary of teaching union the NASUWT, said Pisa was not the be all and end all.
"Pisa is not and must not be seen as the final word on education in Wales," he said.
"It is critical the Welsh government puts the Pisa 2012 study into proportion, uses it to guide and not drive education policy and takes forward its work in a way that reflects the genuine progress and achievements of the education system."