Many computing educators find themselves teaching a subject that is relatively new to them, making access to high-quality, effective professional development (PD) essential. However computing education research does not always unpack the approach being taken to PD, which may reflect underpinning values and beliefs about teachers’ role in the process. The study reported in this paper set out to explore computing PD opportunities using Kennedy’s framework of transformative, malleable and transmissive PD, whereby ‘transformative’ PD refers to approaches that encourage collaborative inquiry and critical professionalism. In the study, 341 computing teachers in primary and secondary education in the UK and Ireland reported on PD they had considered impactful. Results showed that most teachers highlighted transmissive forms of PD as being impactful, primarily delivery-focused training courses, and only 18 teachers described PD categorised as transformative. Most teachers reported that PD was impactful if it built on their prior knowledge. As it is likely that many PD programs are designed around transmissive approaches to PD, we argue that computing teachers should be supported to engage with a broader range of PD opportunities, particularly those that are focused on inquiry and teacher agency.