In this paper we investigate the link between the language in which pupils take the Programme for International Student Assessment (PISA) test and the scores they achieve in this assessment, focusing upon the case of Wales. Using five rounds of PISA data and an instrumental variable approach, we show how pupils who took the test in Welsh score around 0.3 standard deviations (30 PISA test points) lower in reading, mathematics and science than their peers who took the test in English. This finding is robust to different model specifications and statistical approaches. We argue that this may indicate that the academic performance of teenagers in Wales may be underestimated in PISA -particularly amongst those who take this test in Welsh.
K E Y W O R D Shome language, PISA, test language, Wales | 421 THE IMPACT OF TEST LANGUAGE ON PISA SCORES. NEW EVIDENCE FROM WALES Notes: All OECD recommended practices (final student weights and balanced repeated replication (BRR) weights) have been employed. The "-" indicates that there are no data for that region in the PISA cycle.