Education remains the trickiest part of attempts to reform the public sector. But as ever more countries embark on it, some vital lessons are beginning to be learned.
In many countries education is at the forefront of political debate, and reformers desperate to improve their national performance are drawing examples of good practice from all over the world.
Why now? One answer is the sheer amount of data available on performance, not just within countries but between them. In 2000 the Programme for International Student Assessment (PISA) at the OECD, a rich-country club, began tracking academic attainment by the age of 15 in 32 countries.