The Organisation for Economic Co-operation and Development's publication Education at a Glance compares the performance and outcomes of 26 national systems of education. It is widely used by policy-makers and politicians and covers most of western Europe, the United States, Canada, New Zealand, Australia and Japan.
At a conference in London the UK was taken to task by Tom Healy, acting director of the OECD's International Indicators of Education Systems project. He said there were a number of concerns about the way the UK supplied data for the guide.
For example, it records that 68 per cent of the adult population have completed upper secondary education. This figure is above the average of 55 per cent and second only to Germany in Europe. But it appears that this score was reached because 25 per cent of it covers people who have passed GCSEs and national vocational qualifications level 1, which should be classified as lower secondary examinations if compared with the school systems elsewhere.
The result is that GCSEs are being counted as equal to such qualifications as the French baccalaureate and the German Abitur which are taken by older students. Once this disparity is accounted for, the UK's position plummets to near the bottom of the table.
In his paper for the Statistics' Users Conference, Mr Healy said: "It may be argued that a significant proportion of students with GCSE are as well educated as a majority of students with the highest upper secondary completion in other countries.
"However, in the absence of data to support this, it seems reasonable to assume that there is a significant qualitative difference between GCSE and the upper-secondary qualifications in other countries," he said.
The inclusion of GCSEs and O-level equivalents, he added, had caused problems in other tables in the report when comparisons were made.
Denis Allnutt, director of analytical services at the Department for Education and Employment, agreed there was a problem about where to put GCSE figures. He said international comparisons were never going to be perfect but classifications were under review.