Learner engagement is essential for deep and sustained learning, yet it is seldom included in empirical frameworks for effective continuing professional development (CPD), which tend to privilege broad design features over learner-centred strategies. In this critical case study, I consider this gap by applying the lens of self-determination theory (SDT) to analyse in depth what one U.S.-based teacher described as a transformational professional learning experience. Observing the ways in which learner engagement and facilitators' pedagogical practices combine to satisfy SDT's basic needs of autonomy, competence, and relatedness and to shape this teacher's practice, I suggest that relational responsiveness -- what the focus teacher in this study calls 'regard' -- is an important and under-theorised quality in powerful professional learning. I conclude with theoretical and practical implications for the design and study of continuing professional development.