There is a general consensus that design-based research (DBR) is a genre of approaches in education research to design interventions for specific problems with the aim to gain an understanding of how they work in the problem context. While there is a considerable body of literature discussing the epistemic and methodological aspects of DBR, we found little guidance on how to actually design an intervention. The majority of research articles about DBR projects focus on the output of the projects rather than the process. In this article, we reflect on our approach to design processes in two DBR projects, with a particular focus on making and grounding design decisions. Our aim is to provide support to other researchers engaged in DBR projects and to contribute to a discussion about practices in DBR to contribute to design methodologies. We conclude with three key contributions. First, we emphasize the significance of awareness of design decisions as well as their groundings, advocating for thorough consideration of the applicability of theories, and transferability of empirical findings, as well as pragmatic and personal factors. Second, we recommend a flexibility in revising design decisions, allowing for meaningful refinement of interventions in response to evolving contexts and insights. Third, we propose a systematic approach to arrive at and document design decisions, facilitating communication within DBR projects and across research communities.