This paper traces the development of responsive facilitation practices in online teacher communities focused on analyzing video artifacts of K-8 mathematics instruction. The study was part of the Responsive Math Teaching project, a research-practice partnership focused on improving mathematics instruction in a network of 14 under-resourced urban elementary schools. As part of the model for the development of instructional leadership, grade-level Collaborative Lesson Design groups engaged in regular cycles where they met online to plan a lesson, enacted that lesson in their classrooms, and then met again to debrief. Each group was composed of a university-based mentor, novice teacher leaders who were learning to facilitate the sessions, and teacher participants. Drawing on a situated perspective, we explored the following questions: What is involved in facilitating the sharing of video artifacts in online teacher learning communities? What are the component responsive facilitation practices? How do developing leaders use of those practices develop over time? We draw on our analysis to develop a framework that articulates how teacher leaders learned to facilitate discussions in ways that built on teacher knowledge, experiences, and contributions while also focusing on a professional learning goal. Paper Presented at the 2023 Annual Meeting of the American Educational Research Association