This paper presents the research work carried out by an interdisciplinary group of technologists and entertainment experts in collaboration with primary teachers to develop a serious game to work primary education-oriented competences. The serious game called 'Ferran Alsina' is conceived as a tool to develop competences in the primary education program. To design this game, 25 primary school teachers helped the technical and investigative team in a co-creation activity executed with the methodology named Action-Research. This allowed the implementation of competences inside the game's playability and narrative.