This document describes a study that used social network analysis to investigate participation patterns in two phases of the CALIBRATE online collaboration project. Teachers from several European countries collaborated online to evaluate and create learning objects for a digital learning repository. In Phase One, 23 teachers collaborated in subject-specific groups over email and a virtual learning environment. In Phase Two, 20 teachers collaborated in one group in a different virtual environment. The study analyzed message logs and interaction data to identify the most active/passive participants, how balanced participation was, how dense the networks were, and the role of the online facilitator. Key findings included identifying central and peripheral participants, how participation balanced changed across threads and phases, and that the facilitator's role evolved during the