<p>This study investigated the relationships among socio-emotional climate, positive interdependence, and group outcome among pre-service teachers participating in an eight-week online collaborative instructional planning (CIP) project. Furthermore, it examined the moderating effects of group composition – gender and group history – on these relationships. Participants completed the Group Processes Scale assessing their perceptions of socio-emotional climate and positive interdependence. Considering the nested data structure, hierarchical linear modeling (HLM) analyses were conducted to predict socio-emotional climate, positive interdependence, and group outcome. The study revealed a significant and strong positive relationship between socio-emotional climate and positive interdependence, indicating that each mutually enhances the other in online CIP. Both socio-emotional climate and positive interdependence were significant predictors of group outcome, while their effects were especially evident in “all-male” groups, as well as in groups with no prior collaboration history, suggesting that group composition factors can amplify the benefits of group dynamics. These findings underscore the importance of fostering both positive interdependence and a strong socio-emotional climate, while strategically considering group composition to enhance the success of online CIP.</p>