From a humble information system wikis have evolved in both business organizations and educational institutions, catering to, among other uses, training and education. The current work focuses on wiki-based learning and aims to address a visible gap in research. Much previous work is but prescriptive guidelines and self-reflections. While attempts exist involving some assessments of wiki-related teams, they use short-term teams and place their concern on only outcomes. We advocate examination of mature teams as well as the interaction process. The current study pays attention to two aspects earlier suggested salient: learners’ prior wiki experience and instructor’s support. It offers in-depth understanding of wiki effectiveness in collaborative learning environments, operationalized using project teams. A theoretical model is developed, proposing wikis to positively affect learning outcomes of self-reported learning, process satisfaction, positive social environment and a sense of community, through the processes of task-related and socio-emotional activities. The model posits wiki experience and instructor support to enhance these activities. Tested using two separate wikis (Mediawiki and Confluence) over a protracted period of one semester, our findings show strong support for wiki effectiveness, contributing to research areas such as wikis and small groups. Implications for wiki development and instructional use are derived.