Background/Context: This article describes how we refined an innovative methodology for equitable collaboration between university researchers and classroom practitioners building and refining theory together. The work builds on other coinquiry models in which complementary professional expertise is respected and deliberately exploited in order to question, understand, and improve practice. Drawing on research using digital video to help make explicit teachers' pedagogical rationale, our approach involved intensive critical scrutiny of video recordings of teachers' own and others' practices. Purpose/Objective/Research Question/Focus of Study: The study explored and reformulated definitions of classroom dialogue--in which teachers and students exchange, evaluate, and build on ideas--in the context of interactive whiteboard (IWB) use. This article focuses on the collaborative theory-building process itself, whose aim was to exploit insights derived from research to stimulate and inform thinking, guide principled development of new classroom practices, and refine the theory. Population/Participants/Subjects: Three university researchers and three (primary, middle and secondary school) United Kingdom teachers, along with their students aged 10-14, took part in the research. The teachers were all experienced, reflective practitioners with an established dialogic pedagogy. They taught personal education, English, and history. Research Design: A case study design was used to collect qualitative observational data. A series of three in-depth workshops focused on the construct of dialogue and critiqued associated literature. Subsequent joint review of lesson videos and other data plus two further workshops served to characterize effective strategies for supporting dialogue. Data Collection and Analysis: The three initial workshops prepared teachers to design and teach three consecutive lessons employing a dialogic approach supported by IWB use. Teacher and university researcher pairs jointly reviewed the lesson videos, along with unstructured teacher diaries, interviews (three per teacher), and other contextualizing data, and two further team workshops took place. Cross-case analysis of the data, including interview and workshop transcripts, follow-up questionnaires, and accreditation reports, characterized teacher perspectives on the reflexive--and itself dialogic--coinquiry process and its outcomes. Conclusions: Preconditions, critical features, and scalable benefits of our evolving approach are identified for other research partnerships. The process additionally yielded negotiated, recontextualized understandings of dialogue and strategies for fostering dialogic pedagogy. These were framed in accessible language, spontaneously shared within the schools and adapted for wider use, thus forming a springboard for further critique and modification in new settings.