An international linking study was conducted in order to link parameters of PISA-based Test for Schools (PBTS) cognitive items to PISA international scales. New booklets for the linking study were designed in which the PISA trend items were inserted as anchor items in addition to the PBTS items. Data was collected from four countries with over 95 000 students via Computer-Based Testing, and analysed with the finite mixture modelling in order to estimate the parameters of PBTS items under the constraint of fixed PISA item parameters. The estimated item parameters were validated in terms of reliability and international comparability. The linking study enabled the PBTS test to provide valid and reliable scores on PISA international scale.