The purpose of this study was to explore 28 Taiwanese fifth graders' development of knowledge on biological reproduction. The students received three weeks of instruction about biological reproduction and were interviewed to determine their cognitive structures. The interviews were conducted three times, at weekly intervals throughout the instruction, and an additional interview was conducted two months after the instruction. The interview data were analysed through a flow map method to show cognitive structure, and the students' information processing strategies, derived from an analysis of the flow map data, were also explored. The results suggest that there are three stages of cognitive structure development. In the first stage, categorised as ‘knowledge development’, both the extent of knowledge and the richness of networking of ideas increase. In the second stage, categorised as ‘knowledge extension’, only the amount of knowledge continues to increase. In the final stage, called ‘knowledge refinement’, the amount of knowledge recalled decreases, while the richness in networking of ideas remains stable. At the same time, the use of higher-order information processing modes (e.g., narrative containing statements inferring and explaining) increases dramatically. This implies that the rich connections between concepts and the use of higher-order information processing strategies may facilitate maturation of connected knowledge in memory.