In this paper I address the use of digital tools (GeoGebra) in open ended design activities, with primary school children. I present results from the research and development project “Creative Digital Mathematics”, which aims to use the pupil’s development of mathematical board games as a vehicle for teaching skills with GeoGebra, as well as an entrepreneurial attitude towards mathematics. Using the instrumental approach I discuss how open ended transdisciplinary design activities can support instrumental genesis, by considering the extent to which the pupils address mathematical knowledge in their work with GeoGebra and how they relate their work with GeoGebra and mathematics to fellow pupils and real life situations. The results show that pupils’ consider development of board games as meaningful mathematical activity, and that they develop skills with GeoGebra, furthermore the pupils considers potential use of their board game by classmates in their design activities.