This study examined a wiki as a computer-supported collaborative learning (CSCL) environment at upper primary level. A total of 388 Hong Kong Primary-five (P5) students in four Chinese primary schools used a wiki platform within the context of their group projects in General Studies (GS) classes. Adopting a mixed-methods design, qualitative and quantitative data were collected from focus group interviews, survey and wiki entries. Findings showed that the wiki platform provided educational, technological, and social affordances for the P5 students' collaborative learning. At the same time, constraints were found to be related to technological factors and users' dispositions, which may be counterbalanced by providing scaffolding and selecting wiki variants. Students' attitudes towards the pedagogical value of the wiki were found to be strongly positive after the group project implementation. Overall, this research contributes to the literature on the use of wikis in primary education. (Contains 6 tables and 1 figure.)