The current contribution focuses on evaluation research as a process of learning and development for practice, by looking at conditions of collaboration between practice and research in two examples. We exemplify that learning from evaluation in complex programme settings is related to the nature of the collaboration between social work agencies and researchers. Findings are based on two similar cases of evaluation research for interagency collaboration in Germany and Slovenia. Results show that a symbiotic collaboration between research and practice enhances the learning and development potential for practice, but also that the balance between organizing the collaboration process and leaving room for experimental and ad hoc decisions needs to be guarded. Both advantages and disadvantages of planning and stability need to be taken into account when doing practitioner evaluation research.