education performance to be ranked against others worldwide.
The results will be particularly interesting for the UK because they will be the first to be taken by children who have spent virtually all of their schooling under Labour governments in Westminster and Cardiff, making them a key barometer of New Labour's performance.
In Wales, participation in the Organisation for Economic Co-operation and Development's tests was a key recommendation of the 2004 Daugherty report that led to the abolition of key stage testing. Around 130 Welsh secondaries are taking part.
Across the border, around 4,500 English 15-year-olds, in 190 schools, have agreed to participate in the Programme for International Student Assessments (PISA) tests in English, maths and science - used by the media to rate education systems across the globe, and taken in 57 countries.
This year, the statistically-representative sample of schools had to be bribed to take part. The Westminster government was forced into a desperate campaign to recruit them, after the UK was the only country to be barred from official publication in the last round of PISA in 2003.
That year, many English schools refused to take the tests, partly because of assessment overload and because they were held in April as pupils were preparing to take their GCSEs. The OECD therefore ruled the sample was not large enough for the results to be representative.
The Government then argued successfully for the UK to take the 2006 tests in the autumn. It also offered schools pound;1,000 each to take part, plus the chance to attend a post-testing conference and individual feedback on their results.