Online Collaborative Writing (OCW) is a prevalent practice among undergraduate students, yet challenges arising from a lack of group awareness (GA) often hinder effective collaboration. To address such challenges, this study included three phases: (1) A preliminary study (n=9) aimed to identify challenges that undergraduate students face while engaging in asynchronous OCW. (2) A GA tool (i.e., SITU) was designed to address the identified challenges by allowing students to invite their peers to edit specific sections of the document and provide written feedback. (3) The effect of SITU on students' online writing behaviors and peer editing outcomes was evaluated. Students in the experimental group (n=32) worked on an OCW task with SITU while students in the control group (n=30) worked without it. Employing a mixed-methods research design, data were collected via screen-capture recordings of students' writing processes and group interviews. Results from the preliminary study revealed that students experienced discomfort in editing parts of the shared document written by peers and encountered difficulties in coordinating task-related activities. The main study revealed that collaborative writing with SITU led to an almost twofold increase in the time students spent on conducting major edits to paragraphs written by peers.