Pisa tests: What do we know now?
The results of the latest Pisa tests, launched by the OECD this week, are going to be analysed disputed and selectively quoted for the next three years.
But what have we found about the world's education systems, from these tests taken by 15 year olds in maths, reading and science?
The coverage has been dominated by the rise and fall in national rankings, or in the UK's case getting stuck in the middle.
But there were also overarching findings from this mammoth trawl of data, based on 500,000 teenagers in 65 countries and education systems.
For instance, behaviour in class is better now than three years ago.
And among better-off countries, the amount spent on education does not seem to have any clear link with improving results.
But there were other more specific lessons.
East Asia's success not 'cultural'
The runaway success story has been the achievement of a clutch of Asian education systems. But results saw the OECD's Andreas Schleicher challenging any stereotypes about some places having an inherent "culture" of education.
Results in Shanghai and Vietnam are much better than three years ago, he says, but the "culture" hasn't changed.
The improvements reflect a deliberate policy of ensuring that a high proportion of pupils will succeed.
This also applies in other parts of the world. Poland has been transformed into one of the best school performers in Europe and the OECD argues this reflects an active policy of change and not any inherent quality of its culture. The implication of this is that other countries could follow their example.
High results or happy children?
Is it a good thing to be successful at any price? South Korea might be at the top end of the performance tables, but it's at the very bottom in how happy pupils are in school. Punishingly long hours of study, high pressure tests and extra lessons out of school might deliver high results. But is that the system to pursue?
In contrast, Peru, Albania and Indonesia, among the lowest test performers, have the highest proportions of children who like being at school.
And the Pisa study also showed no clear link between parental choice and better standards - but would parents accept a more controlling, centralised system to raise results?
Expect more examination of the relationship between cramming, creativity, choice and happiness.
Irresistible rise of rankings
The impact of Pisa as an international phenomenon could be directly linked to its bold willingness to rank countries. These league tables emerged about the same time as universities first experienced being listed like football clubs. It was an unfamiliar approach, but ranking has spread like ivy over ancient institutions. Everyone stands back and says it's a terrible over-simplification - and then starts planning ways to get higher.
Seekers after educational excellence once used to head pilgrim-like towards Finland. This was the most quoted example of a high performing school system, even though in many ways it was a very distinctive and individual system. Scandinavia was the education world's sensible successful neighbour.
But Finland has slipped downwards and the gloom has spread across Nordic countries, with Sweden among the biggest fallers. Norway and Denmark are absent from the top end of the tables. Their sluggish performances has been overtaken by countries such as Estonia, Poland and Ireland.
Are regions a better way of measuring results?
The headline results for these tests are about the performance of countries or at least big Chinese regional education systems that are as big as countries, such as Shanghai or Hong Kong.
But this year's results show much more local detail. And it often entirely contradicts the national picture.
For instance, the education system in the United States has been seen as one of the great under-performers, struggling among the below-average stragglers.
Go down to state level and it can be an entirely different story. Massachusetts would be a match for the best European systems. There are similar examples in Italy and Spain. Wales is a long way behind the other parts of the UK.
What this means, the OECD says, is that there are often bigger differences within countries than between countries. And if one region can perform so well, why not the rest of the country?
Education systems are inextricably linked with economies and the ambitions of their people. And the rising stars are those that are pushing up from below, in Asia, South America and eastern Europe. Vietnam, Brazil are Poland are getting the praise for progress, following in the footsteps of Singapore and South Korea.
Baltic states such as Estonia are now more likely to be among the top performers than wealthier western European countries.
The great powers of the 20th Century are conspicuous by their absence from the top of these education rankings. The UK, France, Russia, the US, all with very different systems, have collectively shown no sign of a resurgence. They each will have a complicated, entrenched set of legacies. Expect more political introspection and rummaging through the ideas box.
Rise of global tests
Where is this all heading? Economies, employers, digital technologies and media operate globally across international boundaries.
But education has until recently remained stubbornly inward looking, with national systems only measured against national exams. Pisa has thrown down a challenge on their credibility.
What happens if national exam results are going up when international tests are staying flat? And how can we rely on the accuracy of a sample-based process such as Pisa? More examination of the examinations is lying ahead.