This research involves two case studies, one in Melbourne, Australia the other in Gothenburg, Sweden, that focus on how using observation tools to gather classroom evidence of teaching and learning promoted opportunities to discuss and develop professional practice. We found that dialogues between pre-service teachers and more experienced practicing teachers after an observed lesson were richer and more nuanced in their feedback when evidence was gathered and presented in a common way. The feedback provided in these dialogues was utilised in an ongoing manner when the evidence took the form of an observation tool that was provided to the pre-service teachers. Crucially these observation tools prompted pre-service teachers and their supervising teachers to attend to evidence of learning in their classes and make their reasoning and choices in practice transparent. The concepts of relational agency, communities of practice, and practice architectures provide the analytic framework for this study. Our findings suggest that in both cases formalisation of evidence-informed professional dialogues between pre-service teachers, mentors and others, can create further opportunities for professional development, provide a safe framework to interpret and expand the 'object of activity', and gain deeper understanding of the 'doings, sayings and relatings' in communities of teaching practice.