Pedagogical conversational agents (PCAs) are intelligent dialog systems that can support students as chatbots or voice assistants. However, many users find interactions with PCAs less engaging. One solution to increase learners’ engagement is to embed the PCA in a virtual world, e.g., as a humanoid avatar that facilitates collaborative learning. Such a learning setting could be beneficial because virtual worlds positively affect fun and immersion. In this paper, we derive prescriptive design knowledge for PCAs in virtual worlds based on the results of nine expert interviews synthesized with findings from the literature. This design knowledge aims to enable the meaningful design of PCAs in virtual worlds. We contribute to research and practice by demonstrating how PCAs in virtual worlds can be designed to increase students' motivation to learn.