The project studies the characteristics of the StoryCircles process of professional development and its potential opportunity for secondary mathematics teachers to learn through lesson-focused collaboration. In StoryCircles, teachers draw on each other’s knowledge to anticipate and design how a problem-based lesson could unfold. Their anticipations are then prototyped in storyboards to enable teachers to visualize and argue about various decisions a teacher could make along the timeline of the lesson. In this iteration of StoryCircles, teachers initially work together for one cycle to produce a first draft of a lesson storyboard which is then annotated by teams of secondary mathematics teachers—half of which are gathered from the United States and the other half gathered from four different partner countries (Canada, India, Philippines, South Africa). The annotations provide feedback to the original group of teachers as they engage in a second cycle—arguing about lesson decisions and contingencies and revising their first draft designs for the lesson. Because teaching is cultural, we hypothesize that both the nature and focus of the feedback provided by domestic and international teams will differ in terms of how they feed back to the authoring team. The project brings together researchers, professional development facilitators, and teacher educators across the U.S. and partner countries to examine the potential of StoryCircles for supporting teachers’ professional growth. We ask how the storyboards and annotations of storyboards serve as opportunities for teachers to learn within StoryCircles—reflecting critically on their own practice and seeing, in others’ contributions, alternative approaches to practice. We also ask what is the variability among the differently-sourced annotations on lessons and what do different annotations make available for teachers to learn.