Pisa tests: Wales and Scotland 'dragging UK performance down'
Wales and Scotland's results in a major study of educational performance are "dragging the UK down", the chief inspector of schools in England has said.
Ofsted boss Sir Michael Wilshaw told the BBC News Channel that Welsh education is "paying the price" for abandoning standard assessment tests.
The Pisa tests are taken by 15-year-olds every three years.
The Welsh Government said a "radical overhaul" of education was under way.
Welsh students ranked below the average of 72 countries taking part in the tests in science, reading and maths.
For the fourth time running, they also did worse than their counterparts in England, Scotland and Northern Ireland.
Scotland's schools recorded their worst ever Pisa results, with all three subject areas being classed as "average".
Sir Michael Wilshaw said: "England's results are, I think, pretty good. The focus of Pisa this year was science and we've improved our position from 21st to 15th.
"We're doing better than the other home nations - Scotland and Wales. Their results are dragging the UK performance down a bit."
He added: "I remember when the Welsh Government took away all the accountability measures that we have in England - Sats, testing and so on - and that was disastrous, absolutely disastrous and Welsh education is paying the price for that.
"We didn't do that in England. We kept the testing at [ages] seven, 11, 14 and we kept accountability and that's what the Welsh system lost."
Wales abandoned Sats and school performance league tables in 2004.
National reading and numeracy tests were introduced as part of a raft of reforms brought in following the 2010 Pisa results.
First Minister Carwyn Jones admitted in a heated session of the assembly on Tuesday that the results make for "uncomfortable reading".
Education Secretary Kirsty Williams said Wales could do better, adding that plans - including a new curriculum - were in place.
Scottish Education Secretary John Swinney said the results showed that "radical reform" was needed if Scotland's education system was to become world-class again.
A Welsh Government spokesman said: "We are currently engaged in a radical overhaul of our education system to raise standards and the aspirations of our learners.
"This includes introducing a new curriculum, numeracy and literacy tests, categorisation and more robust qualifications to give pupils the skills they need to succeed in life."