International comparative assessments of student achievement are constructed to assess country-level differences and change over time. A coherent understanding of the international trends in educational outcomes is strongly needed as suggested by numerous previous studies. Investigating these trends requires long-term analysis, as substantial changes on the system level are rarely observed regarding student outcomes in short periods (i.e., between adjacent international assessment cycles). The present study aims to link recent and older studies conducted by the International Association for the Evaluation of Educational Achievement (IEA) onto a common scale to study long-term trends within and across countries. It explores the comparability of the achievement tests of the Trends in International Mathematics and Science Study and previous IEA studies on mathematics in grade eight. Employing item response theory, we perform a concurrent calibration of item parameters to link the eight studies onto a common scale spanning the period from 1964 to 2015 using data from England, Israel, Japan, and the USA.