Within the emerging field of research on education for sustainability (EfS), case studies are an important if not the predominant research approach, although often criticised for its lack of internal and external validity and a tendency to draw conclusions with insufficient rigour. While, basic concerns have been expressed and discussed in an early issue of this journal, main assumption still hold true after more than 10 years of research in the field. Only a few approaches so far have tackled the challenge to provide cross-case comparison and the synthesis of case-study results still remains a research desideratum. In this paper, we argue that developments in the field of qualitative and quantitative meta-analysis in educational science offer a framework, which can be used to overcome that shortcoming. After describing the idea of research synthesis, different types of such a meta-analysis are identified and their potential is discussed for existing case studies in higher EfS. This paper concludes with recommendations for further case-study research in the field. (Contains 1 figure.)