This article, updated and expanded from one written for "The Times Educational Supplement", 10 December 2010, asks whether politicians are right to quote the country's performance in international tests in support of such policies as re-introducing O levels. It finds reasons to doubt that the tests give an adequate picture of children's learning, in comparison with either older cohorts or overseas peers. Nor do they provide a fair measure of schools' success or the validity of examination qualifications.