The DaZKom-Video project aims at performance-oriented measurement of German-as-a second-language (GSL)-competence of pre- and in-service teachers using video-based stimuli and oral responses. The present study is part of this project and focuses on the psychometric quality of the DaZKom-Video test instrument and evaluates the dimensionality of the construct GSL competence (Deutsch-als-Zweitsprache-Kompetenz). Additionally, we explore correlations between GSL competence and sociodemographic data as well as learning opportunities. The sample consists of pre- and in-service teachers from different school forms and universities across Germany. The items and scale analyses reveal good psychometric quality: The item-fit to the Rasch-model as well as the discrimination is satisfactory. The dimensional analyses show best model fit for the one-dimensional and three-dimensional models. Test persons with GSL experience such as in-service teachers (in contrast to pre-service teachers), test persons with teaching experience, those with an additional qualification in the field of GSL and test persons with many learning opportunities are statistically more likely to respond to items correctly. These results indicate a reliable and valid test instrument for performance-oriented measurement of GSL competence.