Studies in collaborative learning have shown that collaborative learning is an appropriate model for higher education. The cognitive processes making up collaborative learning include explanation, internalization, conflict, appropriation, shared cognitive load, mutual regulation and social grounding. This paper reports the design and evaluation of a collaborative tool for supporting a distributed collaborative learning activity of a college class. Unique from the pre-existing educational technologies, this tool provides shared documentbased rationale spaces in the group workspace enabling students to document and share their rationales of the documents. The students' experiences of using the tool in their group work were studied. The results show that engaging in the process of documenting.