This manuscript reports a collaborative self-study conducted by three teacher educators who carried out and discussed joint observations of mathematics instruction in preservice teachers' field experience classrooms. We investigated the teacher educator identities that influenced our perspectives on and interpretations of preservice teachers' mathematics instruction. A duoethnographic approach supported us in interrogating ourselves alongside one another and presenting our resulting analysis as a polyvocal dialogue. Transcripts illustrate key identities that shaped our classroom observations (methods course instructor, supervisor, teacher, and researcher) and evolving aspects of those identities (becoming an insider as a supervisor, an outsider-within as a researcher). The transformative stories reported here contribute needed insights into how mathematics teacher educators' identities relate to their practices as supervisors of preservice teachers, an area that has received scant attention in the mathematics teacher education literature.