The current paper combines arguments from the social capital and group cognition literature to explain two different processes through which communication network structures and intra group conflict influence groups' cognitive complexity (GCC). We test in a sample of 44 groups the mediating role of intra group conflict in the relationship between communication network density and fragmentation on the one hand and groups' cognitive complexity on the other hand. The results show that network fragmentation has a positive effect on GCC by fostering task conflict, while network density has a positive impact on GCC by reducing relationship conflict in student groups. The paper makes an important contribution to both theory and practice in the field of collaborative learning, by exploring how groups' affective and a cognitive dynamics impact on emergent collective cognitive structures. (Contains 1 figure.)