Background/Context: This work draws on a "participatory" approach to research collaboration that respects the teacher's "voice" in building on and extending the interactive "colearning" agreements between researchers and practitioners that work toward improving practice. Both parties in these agreements act as agents of (reflexive) inquiry, actively participating in rigorous and systematic joint analysis and contributing interpretative insights. Focus of Study: This article describes and reflects on a collaborative approach to the analysis of digital video recordings of classroom activity. Our primary focus was assisting teachers to make explicit the pedagogical rationale underlying their practice. A key aim was to draw on sociocultural perspectives to develop a shared, grounded account of the processes through which teachers strategically mediate subject learning, in the context of using projection technology. The process of collaboration itself is our focus here. Participants: Four UK teachers, one in each of four secondary subject areas (English, mathematics, science and history), and their students aged 12-15, took part in the research. The teachers were all experienced, reflective practitioners. The research collaboration also involved a colleague of each teacher, two researchers (the authors), and academic subject specialist colleagues. Research Design: A case study design was used to collect qualitative observational data. Data Collection and Analysis: Teachers were observed over six lessons each and interviewed four times. They also collaborated with us in critical scrutiny and discussion of lesson videos during a series of four recorded meetings, making underlying rationale explicit and identifying emerging themes. Student perspectives were sought through two focus group interviews in each case. Copies of student work and all lesson materials and outlines were collected, screen displays were captured, and each teacher kept a diary (unstructured) recording his or her planning, decision making, and/or postlesson reflections. Interview transcripts, individual commentary, meeting notes, and diaries were thematically analyzed using HyperResearch software. Findings: The dialogic process culminated in development of "intermediate theory" bridging between teachers' perspectives on supporting learning in specific settings, and key constructs from sociocultural theory. Hence, a priori theories were elaborated, integrated, and reframed using a common language. Conclusions/Recommendations: The findings are being exploited through coconstruction and dissemination of a set of interactive CD-ROMs. These characterize the key themes and strategies emerging within and across cases, with illustrative video sequences for each case in turn hyperlinked to professional development activities and relevant aspects of the narrative accounts.