Knowledge awareness refers to one's awareness of the other group learners' domain knowledge. CSCL researchers maintain that knowledge awareness is an important aspect to the outcome of collaborative learning activities. Interested in groupware design to support knowledge awareness, I investigated how a shared rationale space affected one's knowledge awareness in virtual collaborative learning environment through a classroom study. In the investigation, a rationale is a learner's reasoning behind his/her decision of the tasks in the learning activity. The findings show that one's awareness of the other group learners' rationales, namely, rationale awareness, enhances one's knowledge awareness. The study suggests several design implications to support knowledge awareness, including sharing one's contextual information that reveals one's domain knowledge; highlighting the association between the knowledge awareness information and the learners who provided the information; and supporting utilization of knowledge awareness information at both individual and group levels.