What countries can learn from PISA tests

IT IS easy to be cynical about school-test results, particularly when you are grading the performance of something as complex as a country’s education system. Undaunted, every three years the Programme for International Student Assessment (PISA), which is run by the OECD club of mainly rich countries, tests more than half a million 15-year-olds in three subjects—maths, reading and science—to give a snapshot of national school-policies.