This study aimed to involve International Baccalaureate (IB) teachers in formative assessment and summative evaluation of a continuing professional development (CPD) programme designed to facilitate a student-centred, process-focused approach in which the ‘Approaches to Learning’ (ATL) element of the IB curriculum takes a central role. Given its emphasis on participants’ collective perspectives, focus groups were selected as the data collection method. Respondents were twelve teachers with diverse backgrounds and experience, from different school departments, with varying teaching styles, epistemological beliefs and views regarding ATL. This study includes a discussion of the literature with reference to teachers’ beliefs, attitudes, values and knowledge, the role these play in teaching practices, the extent to which CPD may be able to influence them, and the elements of CPD which make teachers’ development more likely.Findings indicate that formatively assessing teachers’ development from CPD, and development itself, are ‘messy’ processes, as is trying to distinguish between ‘student-centred’ and ‘teacher-centred’ teaching in relation to facilitating self-regulated learning. Differences were identified in how experienced teachers, particularly those with Postgraduate Certificate in Education (PGCE) certification and new teachers, particularly those without a PGCE, reacted to CPD and developed in relation to the aims of CPD. However, these issues were mitigated over time by the CPD programme’s emphasis on collegiality and its coherence with previous CPD and IB standards for teaching and learning. Students’ increasing competence with, and acceptance of, student-centred teaching also made it easier for teachers to develop their practice, illuminating the nature of enculturation as a driver of learning. Importantly, formative assessment helped the researcher to understand the complex and incremental nature of teachers’ development as well as gain insights into how CPD contributed to that development. This investigation demonstrates that brief experiences of top down, whole school, ‘training model’ CPD can, indeed, enhance teachers’ student-centredness and facilitate explicit instruction of ATL skills, and illustrates the utility of using focus groups to formatively assess, and summatively evaluate, teachers’ CPD.