This study analyzes the collaborative writing sessions of two groups of advanced diploma economics students with mixed proficiency. Although studies in collaborative writing usually highlight the mixed results of students' collaboration ranging from promoting peer learning to having unresolved conflict, the findings of this paper only provide the advantages gained by the students in this study. It is attributed to the use of a group learning contract which the students signed before collaborating with their friends. The students' collaborative writing sessions of long reports were video-taped and they were followed by the production of student diary entries and interviews in order to understand the experience gained during the sessions. Furthermore, the instructor's reflections were analyzed to increase the understanding of the group dynamics which had occurred. The findings show that all students had mutually benefited from the collaborative writing sessions. The benefits gained are heightening their sense of responsibility towards the task, promoting the sharing of new information, allowing the sharing of expertise, helping narrow down information, and negotiating successfully by using Facebook as a means to continue their discussion on matters which they had difficulty in resolving through face-to-face interactions. (Contains 8 tables.)