The authors report outcomes of an evaluation of a 'video club' intervention to improve the feedback and dialogic teaching practice of 91 teachers from 11 primary schools in England. Participating teachers worked collaboratively in a sequence of six video clubs over a six-month period. To understand teacher engagement they examine videos of video club meetings; online platform use metrics; surveys; selected videos of classroom practice; focus groups; and interviews. They evaluate change in teachers' thinking and practice using survey results for participants compared to a comparison group of non-participating teachers at the intervention schools. The survey includes a new instrument for gathering evidence of teachers' thinking and practice in feedback. The results suggested changes in thinking and practice for teachers who self-reported as engaging highly with the intervention. They conclude by discussing the potential of video technology within professional development and the challenges of researching changes in thinking and practice.