Using asynchronous online discussions for interschool collaborative project work represents one of the innovative practices in the Singapore classroom. With anytime, anywhere access to interactions among the students and teachers, the asynchronous nature of these interactions leads to new paradigms for teaching and learning, with both unique problems of coordination and unique opportunities to support active participation and collaborative learning. A research study was conducted to investigate how primary school students participate and learn in project work based on co-construction of knowledge in asynchronous online learning environments. 10 teachers and 20 students from 5 primary schools participated in this half-year long research study. Teachers crafted project tasks for implementation at the students' level and these tasks were addressed collaboratively by the students who formed project groups with members from another school. Quantitative and qualitative analyses of students' activity in the asynchronous online environment were conducted. Students' sent and received notes as well as the frequency of scaffolds used in the online environment were evaluated. Each note was also ranked according to Gunawardena, Lowe and Anderson's (1997) "Interaction Analysis Model". The findings provided evidence to suggest that primary school students participating in the online project work learning environment were capable of the co-construction of knowledge up till Phase IV of the "Interaction Analysis Model". (Contains 5 tables and 4 figures.)