This two-year longitudinal study examined the collective and individual effects of a collaborative video learning lab (CVLL) in a French lower-secondary high-poverty school. The CVLL was designed to: i) determine the learning objects shared by the in-service teachers based on their actual teaching activities and ii) encourage them to participate in a collaborative inquiry on their filmed activity regarding the selected shared learning object, with the goal of supporting them as they appropriate more efficient teaching practices..The participants were novice in-service teachers (n=2) and experienced teacher-facilitators (n=2). Data consisted of cross-analysis of video recordings (n=37) from i) classroom teaching activity (n=11), ii) CVLL sessions (n=6), and iii) teachers’ observations and comments on both (n=20). The results revealed that novice and experienced teachers lived critical experiences in the CVLL regarding the shared learning object and show how they transformed their activity as teachers, mentors or facilitators.