This paper reports the results of a quasi-experimental study that evaluated the effectiveness of collaborative mind mapping in three Hong Kong primary schools. More than 200 grade 4 students, divided into three pedagogical groups, participated in a variety of science learning activities with the aid of a mind map and/or collaborative group work. The results of diagnostic tests reveal the synergy of peer collaboration and mind mapping to be more effective than either collaboration or mind mapping alone in enhancing students' scientific achievement. Analysis of the students' science discourse and follow-up interviews indicates that collaborative mind mapping fosters learning motivation and facilitates the joint construction of conceptual knowledge in science. Recommendations are made for the integrative use of graphic organisers and group work, and implications for future research on science teaching in Hong Kong and elsewhere are further discussed.