This article describes an innovative approach to professional development designed to challenge teachers' pedagogic practice and assumptions about educational technologies such as social media. Developing effective technology-related professional development for teachers can be a challenge for institutions and facilitators who provide this support. To contend with this challenge, we drew on Bain's (2004) "baker's dozen" questions to guide the design of an online postgraduate course for teachers. This article discusses the design of the online course and what teachers came to understand about the relationship between social media and teaching as a result of completing the course activities. This small-scale case study utilised qualitative data from three cohorts of participating teachers and found that teachers do change their pedagogical practice and assumptions about social media for their own teaching contexts when they engage in course activities that challenge their existing mental models and encourage critical reasoning and reflection on learning.