Language-based interaction between learners of German as a second language and their teachers in out-of-class settings such as art museums requires mediation, which in turn influences discourse practices. How L2 learners manage the communicative task of discovering artworks and how teachers can assist and mediate context-specific aspects of interactional competence are the guiding questions in this article.To answer them, this article reports on an exploratory study of an art-and-culture buddy program carried out as part of an interdisciplinary service-learning project at the University of Kassel. One aim of the project was to change the traditional format of guided tours for larger groups and to develop, test and evaluate a supportive and language-sensitive programme for German as a second language learners. The reconstructive case analysis of art communication enables conclusions about the epistemic and linguistic phases in talking about art and the possibilities of scaffolding. An analysis of a dyadic setting provides insights into the professional and linguistic discourse practices in talking about art.