Some studies have reported that the initial music training of primary teachers can be problematic due to gaps in disciplinary and didactic training and a relative neglect of the objectives that music education should address in the school curriculum. Such gaps may lead to low levels of self-confidence in teaching music in the general classroom. Furthermore, the fast transformations occurring in contemporary society in terms of access to and functions of music, demand novel pedagogical approaches that might be better equipped to address current social and educational needs such as creativity, collaborative work and interdisciplinarity. In order to investigate the relationship between the initial musical training of primary teachers and their self-confidence in teaching music, a study was carried out based on an intervention in the Primary Education Teaching degree program at a Spanish university. The intervention was innovative and based on a collaborative, creative, and interdisciplinary approach. The findings, referring both to the processes and products of this intervention, show both an increase in pedagogical reflection and in the transformation of values and beliefs, as well as an improvement of self-confidence in student teachers' musical skills.