Examining Student Participation in Two-Phase Collaborative Exams through   Video Analysis
  In this study we coded, for individual student participation on each question, the video of twenty-seven groups interacting in the group phase of a variety of two-phase exams. We found that maximum group participation occurred on questions where at least one person in the group had answered that question incorrectly during the solo phase of the exam. We also observed that those students that were correct on a question during the solo phase have higher participation than those that were incorrect. Finally we observed that, from a participation standpoint, the strongest (weakest) students seem to benefit the most (least) from heterogeneous groups, while homogeneous groups do not seem to favor students of any particular performance level. 
Joss Ives, Matias de Jong Van Lier, Nutifafa Kwaku Sumah, Jared B.   Stang
physics.ed-ph