This study presents an innovative pedagogical approach where teachers become game designers and engage in creative teaching practices. Within co-design training workshops, 21 Spanish primary and secondary school teachers have developed their own Game-Based Learning (GBL) scenarios, especially tailored to their teaching contexts and students profiles. In total, teachers developed 13 GBL scenarios and put them into practice in teaching contexts. The present paper analyses the impacts of this learner-centred game design approach on teachers' creativity from three different points of view: the GBL design process, the GBL scenario, and the teaching processes at stake. (Contains 1 figure, 4 footnotes, and 2 pictures.)