In educational design research projects, there are long-term relationships between researcher and participants. Hence, in addition to external ethical engagement, researchers have to engage in internal ethical issues, which became evident when a researcher suggested mathematical content for an intervention. The suggestion was both appealing to and uncomfortable for the teachers, and this ambiguity made power relations between the researcher and the participants visible. In the moment, the researcher made decisions about the content that might not be the best. This situation made visible the importance of internal ethical engagement in advance, for example, by thinking about how we care for our participants and for what and whom we are responsible.