It's a breathtaking concept -- but for the OECD, it's a very real way of finding out how well-prepared today's students are to participate in society. If you're not quite sure what PISA is or does, and you've got about 12 minutes to spare, grab a comfortable chair. This video will help you to understand why the OECD's number-crunchers trigger such intense debate about the state of education around the world every time they release the results of the latest PISA survey.