Standardised tests help measure student's progress at school and can inform education policy about existing shortfalls. However, too much testing could lead to much pressure on students and teachers to learn and teach for a test, something that would take the joy out of the learning process. Many parents and educators are all too familiar with this quandary: they recognise that good measurement can drive improvement, but often argue that too much testing can make students anxious without improving their learning. In particular, standardised tests that determine the academic and life pathways of students may trigger anxiety, and if conducted too frequently might lead to poorer performance, absenteeism and lower self-confidence. But are standardised tests really used all that frequently? And what do PISA data show about the relationship between performance, anxiety and the frequency of testing?