The purpose of this study is to investigate the relationships among students' conceptions of knowledge building, approaches to knowledge building, knowledge-building behaviors and learning outcomes. A total of 48 primary school students (from grades 3 and 4) who had experienced knowledge-building activities participated in the present study. After analyzing the students' interview responses using the phenomenographic method, qualitatively different and hierarchically related conceptions and approaches were revealed. The results indicated that the students with fragmented conceptions tended to use surface approaches to knowledge building while those with cohesive conceptions tended to adopt deep approaches. The findings also indicate that the students with cohesive conceptions or deep approaches were more likely to have better learning outcomes than those with fragmented conceptions or surface approaches.