Research on teacher professional development is extensive but there are fewer studies about the practitioners who facilitate professional development. Here we report on a pilot programme for professional development facilitators rooted in a cycle of action research. Informed by a categorisation of professional knowledge and skills of facilitators, in the "developing the developers" programme, professional development facilitators enquired collaboratively into their practice using video observation and peer review and engaged with theories of professional learning. The impact of the programme was evaluated using a framework based on Clarke and Hollingsworth's interconnected model of teacher professional growth. The programme was effective in allowing participants to gain insights into their practice to develop it further and to identify their learning needs. The latter related to improving facilitation skills and knowledge and to improving knowledge about professional development. The interconnected model was found to be applicable to professional development facilitators with some adaptations. Its use enabled understanding of the impacts of the programme and the learning processes involved. Although limited in scale, our study offers a model for professional development that is potentially useful in other contexts. Further, the theoretical frameworks developed may support the design and evaluation of similar programmes.