This paper refers to the work of S J Prais who questioned the outcomes of the Organisation for Economic Cooperation and Development's PISA survey of the reading, mathematics and science attainments of fifteen year-olds. Prais suggested that methodological flaws in Programme for International Student Assessment (PISA) had resulted in an apparent improvement in the attainment of British students, particularly when compared to their Swiss and German counterparts. This paper responds to Prais's criticisms, noting that when Prais's conjectures are tested with empirical data they are not supported. The author argues that many of Prais's criticisms are due to an incomplete understanding and knowledge of the methodology of international studies, and of PISA in particular.