In this study, we investigated the process of teacher co-planning. We examined two teams of high school science and special education teachers brought together to co-plan inclusive, inquiry-oriented science units as part of a professional development effort. We used three conceptual lenses to help make sense of this process: (1) characteristics of collaboration, (2) small group interactions, and (3) community discourse. Using these lenses individually and collectively, we identified strengths and limitations in teachers' co-planning efforts. A strength was that all teachers, irrespective of discipline, shared ideas and helped make decisions about the content and activities included in unit and lesson plans. A limitation was that teachers, again irrespective of discipline, discussed science education topics in their teams more often than special education ones. We found this latter finding of note as it spoke to issues of parity among teachers during the professional development. In our discussion, we argue that each conceptual lens yielded both unique and common findings on co-planning. We also provide recommendations for professional developers and educational scholars intent on organizing and/or researching co-planning among science and special education teachers.