This article describes an innovative continuing professional development (CPD) programme for experienced English for Speakers of Other Languages (ESOL) teachers, and a research study into its impact. The programme incorporates the principles of Practitioner Research (PR) and focuses in particular on the skills of data analysis and situated sense-making. Participating teachers engage in aspects of the research process in a way that builds on and extends their existing professional expertise. The paper sets out the ESOL and wider language education research and teaching methodology background. This includes both conventional and teacher research practices, which underpin the design and implementation of the CPD programme. The discussion section identifies particular strengths of this approach to CPD--the value of collaborative discussion of videoed classroom episodes in workshops, the profiling of context and identity, the recognition of the complexity of classrooms, and the opportunity to engage with the teacher's contribution in developing course cohesion and continuity over time. There are also further challenges: dealing with the time demands of collaborative learning in the CPD context, drawing on selected texts in order to complement teachers' own analyses of classroom interactions; and using opportunities for online communication as part of the CPD process. These insights focus primarily on the social dynamics of the group, issues of participant identity and the teachers' management of relationships, and the overarching meta-themes which teachers draw on to provide coherence to the learning experience. (Contains 5 notes and 4 figures.)