Pisa study: How good is Scotland's education system?
It can be hard to compare the education systems of different countries. Youngsters in different countries start school at different ages, progress at different rates and sit different exams.
But one way of attempting to make a fair comparison comes from the Organisation for Economic Co-operation and Development's (OECD) Programme for International Student Assessment (PISA) results, which are published every three years.
Around 510,000 15-year-olds in 65 countries and economies across the world are tested on reading, maths and science.
Since the teenagers sit similar tests, it is fair to compare the data from different countries and work out which nations are doing well and which are underperforming in these specific fields.
In Scotland the picture is mixed.
Compared to the rest of the UK, Scotland seems to be doing perfectly well. Similar results overall but slightly ahead of England in reading and maths and a little behind in science.
But the international comparison - which many would contend is of more importance and what this data is designed to show - is far less flattering.
The whole of the UK is classed as one country - even though the school systems vary in each nation - but with Scotland's performance so similar to England's this makes little difference to the world ranking.
The UK overall is in 26th place for maths, 23rd for reading and 21st for science. This is the first time the UK has not been in the top 20 for any of the three subjects.
Meanwhile, the tables are dominated by Far East cities and countries - including Shanghai, Hong Kong, Singapore, South Korea and Japan - although closer to home Finland, the Netherlands and the Irish Republic also do well.
South of the border, the Westminster Education Secretary Michael Gove sees the UK's performance as a wake up call and a good reason to justify controversial changes to the education system in England which include a return to more traditional exams in some subjects and changes to the National Curriculum.
Many within Scottish education play down the significance of the PISA rankings. They argue that the tests only cover very specific skills. In particular, they pay no attention to the concept of deeper learning and understanding - a vital concept in Scotland's Curriculum for Excellence. The thought is that deeper learning - truly understanding a subject rather than just giving a youngster facts and figures - equip them far better for the world of work or later study.
Scottish teachers' unions and the General Teaching Council caution against reading too much into the PISA tables. And while opposition politicians may draw attention to the need for improvements, the radical changes in education in Scotland in recent years have enjoyed broad support across the political spectrum. Only the details and the practicalities have caused rows.
But some would note that many of the countries ahead of the UK in the PISA tables are the countries Scotland and the UK increasingly has to compete against in a global economy. Their fear is that Scotland and the UK could ultimately lose out to better equipped workforces.
There is also the question of whether the international rankings reflect the strengths and weaknesses of the school system itself or wider cultural factors: societies where children have a longer school day or spend a greater amount of their time outside school itself studying. Often these are societies which have made remarkable economic progress in recent decades.
In maths, students in Shanghai scored the equivalent of nearly three years of schooling above most OECD countries.
When it comes to trying to improve performance, many factors can come into play - especially helping tackle the link between deprivation and low academic achievement. The Scottish government points to evidence of progress from the latest PISA research.
And measuring the skills of a workforce is about more than the academic performance of 15-year-olds. Other factors include the wider skills base and the proportion of youngsters who have successfully completed further or higher education.
One crucial thing the PISA tables do not tell us is whether the radical changes to secondary education have made a difference yet. S3 now offers students a broad general education and standard grades are being replaced this year by the new National 4 and 5 qualifications. Youngsters also get more time for other activities including community projects and work placements.
No doubt the next PISA tables in three years time will be looked at closely to see if there's any evidence these changes are making a difference.