One way is to compare results of terminal exams for school-leavers at 18.But this is fraught with difficulty. For a start, the leaving exam may not be representative. In the United States, marks in the American College Test, which measures achievement, are holding steady, but a third of first-year college students require remedial education in reading, writing and maths.
In Germany, the Abitur pass rate under-represents the numbers capable of reaching that level because many pupils choose instead to take an apprenticeship due to high industrial wages.
Establishing whether standards are rising or falling is more difficult still, because it depends on tracking exam results over a period of time in which the questions asked and the marking criteria may have changed.
Hilary Steedman, programme director of the Centre for Economic Performance in London, says it is easier to compare levels at any one time.
A more accurate indicator would therefore seem to be comparative tests such as the Third International Mathematics and Science Study. But even then, performance in two subjects may not reflect standards across the spectrum of subjects in that country. In Singapore, which consistently excels in TIMSS tests, achievement is lopsided with much stronger results in mathematics, physics, chemistry and economics. This may be due to the high value placed on these subjects in Singapore.
Dr Steedman, who led a study of assessment, qualifications and standards in the UK, France, Germany, Singapore and the United States, said that while comparisons with Asian countries are always salutary, the standards expected in Germany and France are impressive too. "The quality of French education is very good, the depth and breadth of learning is far in excess of anything we insist on for our students."
In Germany, she said, most people take apprenticeships rather than full-time schooling but two-thirds of the active population reach a standard equivalent to NVQ level 3, twice as many as in the UK.
America is a different case, because it puts a lot of effort and energy into retaining non-academic pupils to the age of 18. "This means on average they don't reach the level of our sixth formers when in high school. But in the end they get a large number to a higher standard than we do," Dr Steedman said.