Beginning with the original IEA Pilot Study the focus of international comparative studies shifted from qualitative description to more quantitative measures of various aspects of schooling. This shift reflected a change that was occurring more broadly in the social sciences about the same time. This chapter focuses not so much on each of the studies but rather on the developing quantitative methodologies that were used to measure and report student performance. A number of methodological issues embedded in these large-scale international measurements of student achievement are identified and discussed. These include the identification and creation of content frameworks for the assessments, a focus on student achievement versus student literacy, the extent to which an assessment broadly samples the content domain versus sampling specific topics in depth, and the way student and country level scores are created and reported.