The article deals with the collaborative and at the same time empirically based standard setting procedure in an interdisciplinary research project. The project assessed teacher expertise in the field of German as a Second Language (GSL) using tasks on short instructional videos. Based on assumptions from expertise research, we determine thresholds of competence in a theory- and data-based manner using the bookmark method. The procedure uses N = 295 prospective and practising teachers’ test results while also depending on the active participation of relevant experts. We conclude the procedure by describing the competence levels derived in the article along an example test item. Finally, we interpret the competence levels achieved in the sample with reference to teacher training in the field of GSL.