The publication of the latest international education league table has created waves around the world. From Shanghai at the top of the table to Peru at the bottom, the PISA rankings create a lot of discussion about the best way to teach children. In some countries the OECD-led ratings are taken so seriously that education policy has been changed to try to improve national performance. But is the league table really as definitive as many people believe? Ruth Alexander looks behind the numbers. Presenter/producer: Ruth Alexander This programme was first broadcast on the BBC World Service.