Due to the larger amount of field trial survey material in TALIS 2018, a rotated questionnaire design was implemented that required a sample size per country' of 600 teachers and 30 principals from 30 sampled schools for the ISCED level 2 core and each international option. Each participant was required to run this field trial, including administering all agreed upon language versions according to standardised procedures. Technical standards and corresponding quality control measures based on those implemented in TALIS 2013 were in place to ensure that the 2018 study implementation yields data comparable with the 2013 data.