This study investigated the impact of a scaffolding system that connects theory and practice to promote the development of the ability to teach mathematics in 100 future Chilean preschool teachers. The theoretical dimension and the practical dimension of both mathematical content knowledge (MCK) and mathematical pedagogical content knowledge (MPCK) were analysed. Data were collected and analysed following a mixed approach. The results of the study reveal the effectiveness of the system in the theoretical dimension and the difficulties that arise in classroom practices. The critical role of the specialized components of MPCK in the theory-practice articulation is discussed.