This study examined two teacher development cases (middle/secondary school science teachers and elementary learning resource teachers) from which significant professional learning outcomes emerged. Both collectives exhibited characteristic qualities ascribed to complexity theory (e.g., self-organized; bottom‐up emergent; ambiguously bounded). This post hoc analysis provides evidence of the robustness of complexity theory and its applicability to analyzing professional development collectives. A diagrammatic representation is provided as a tool for the development and study of teacher development collectives. Recommendations are offered to researchers and teacher development facilitators to use complexity theory at the outset of their projects.