Certain characteristics of teacher professional learning opportunities are known to promote engagement by teachers; however, the successful translation of new knowledge into inclusive teaching practice remains challenging. A greater understanding of teacher motivation for engagement with professional learning opportunities may assist in understanding why particular opportunities result in changes in teacher practices. Within the co-design process of an online professional learning platform, nine teachers described professional learning opportunities which had led to changes in individual or school-wide teaching practices. Thematic analysis of the transcripts revealed a complex interaction between themes which were conceptualised as external or internal to the individual teachers. However, engagement in professional learning opportunities that led to practice change was strongly mediated by teacher perceptions of the credibility and authenticity of both the content and the person delivering the content. The meta-theme of credibility and "authenticity" is considered in terms of teacher motivation and engagement.