Background: Learning which letters correspond to which speech sounds is fundamental for learning to read. Based on previous experimental studies, we developed a serious game aiming to boost letter-speech sound (L-SS) correspondences in a motivational game environment. Objectives: The goal of this study was to determine the efficacy of this game in training L-SS correspondences in pre-readers. Additionally, an extended version of the game was developed given the importance of handwriting in audio-visual integration. We established whether including a motoric component in the game boosted the letter-speech sound training on top of the effect of the game without the motoric component. Methods: One-hundred forty-five kindergartners were randomly allocated to play either the standard audio-visual version of the game, the motoric version or a control math game. All children were pre- and post-tested on L-SS knowledge and reading accuracy. Results and conclusions: We found that playing the game enhanced pre-readers' L-SS knowledge, but not reading accuracy, after a short, intensive intervention period of 3 weeks. However, children who played the motoric version of the game did not differ significantly from either the standard or the control condition. Implications: This game was efficient in training L-SS correspondences in pre-readers. These results suggest that this game might be useful as a preventive evidence-based intervention for at-risk children in kindergarten who might benefit from a head start before learning how to read. Future studies are needed to examine whether a longer intervention period results in L-SS knowledge being translated into reading skills.