In 2020 a Subject Renewal in Norwegian primary education will introduce a new curriculum with more focus on interdisciplinary teaching. Interdisciplinary teaching emphasizes collaboration between teachers from different subjects. There are no pre-existing solutions to address the complexity resulting from collaboration across subjects. To facilitate the transition from the present to 2020 we state our key research question: How might we support teachers in interdisciplinary project planning? We used an open, user-centered, iterative approach along with more traditional qualitative research methods such as interviews, conversations, observation and co-creative sessions with stakeholders. The result is Samspill. A digital prototype and service proposal exploring how to support Norwegian middle school teachers in collaborative project planning across subjects. Samspill provides transparency by offering teachers a collective overview over all of their schools interdisciplinary projects and giving insight into their colleagues’ work. The projects are set up and planned in a visually and clear way, enabling teachers to share ideas and knowledge. When a group of teachers is finished with a project plan, other teachers can be inspired and customize the plan in order to make a new one. In this way, the focus can always be on creating engaging learning experiences for the students. Our design proposal exemplifies interdisciplinary collaboration among teachers in a concrete and visual way, and can encourage more openness among teachers and leaders towards the changes of the primary education subject curriculum.