Despite the high number of educational games released, only a few games have a strong story that is more than an excuse for players' actions. Furthermore, even fewer story-based games utilise the affordances of augmented reality (AR) to concretise abstract concepts while engaging players.Based on our literature review, we were inspired to merge AR into a story-based educational mobile game for teaching fractions to elementary school students. The game Tales & Fractions was created through a two-phase multidisciplinary development process. In order to successfully integrate AR into a story-based educational game, we employed an adapted version of the Scrum agile software development method implemented by a multidisciplinary team of experts from computer science, pedagogy, design and arts. During the development process, we faced many issues that other story-based AR game developers could meet. We summarised the encountered issues with our solutions which could be useful for developers to avoid common pitfalls and to enrich the user engagement.