Teachers of mathematics in New Zealand are critical to the success of their students. In order for teachers to improve student outcomes, it is important for them to have the necessary skills and knowledge relating to mathematics and mathematics pedagogy, but also a positive disposition towards mathematics. Of concern are the many primary-trained teachers who enter their classrooms each day with negative dispositions towards mathematics, even fearing the subject area. This often dates back to their own schooling experiences. Changing these attitudes, along with levels of confidence and understanding, would appear to be crucial. Professional learning is one method for achieving this outcome. Unfortunately, for teachers with low self-efficacy in mathematics, engaging in a professional learning experience relating to mathematics may be considered a threatening experience. Therefore, the aim of this study was to explore the ways in which a flipped professional learning programme might improve these dispositions of primary-trained teachers, along with their skills and understanding in mathematics, termed “teacher capacity” by Zhang and Stephens (2013). This study adopted an action research approach, due to the alignment of this methodology with the desire to utilise volunteer participant teachers as co-researchers and for them to reflect on and change their practice. Qualitative data collection methods were used as the four participants engaged in a flipped professional learning experience. These qualitative data collection methods included semi-structured interviews with individual participants, blogs, and whole group participation in cluster meetings. Following from this study it was found that the use of this flipped professional learning experience increased the self-efficacy ratings of participants in the focus area of their intervention. It was also found that the flipped approach to professional learning had the potential to allow for and encourage teachers to take greater control of their learning journey in and for the teaching of mathematics, thus encouraging teacher agency. It also had the potential to allow for this learning to occur just-in-time, that is, as and when required by the teachers. Therefore, it is the contention of this thesis that a flipped professional learning programme in mathematics could be beneficial to improving the teacher capacity of primary-trained teachers in mathematics.