Participating in peer-review activities can enhance students’ learning outcomes. However, past studies have not thoroughly explored how student performance in peer-review activities and their open-ended tasks relate to online classes. Using synchronous and asynchronous communication tools, we analyzed how students’ collaborative learning activities and participation in a peer-review activity are associated with their learning outcomes in an online undergraduate course. By developing open-ended tasks in small groups, students created Open Educational Resources through a series of peer-review activities. Students’ contributions to collaborative activities were assessed using self-reports and a questionnaire. The findings highlighted the importance of active participation in peer-review activities in online learning that combine synchronous and asynchronous communication tools, which can enhance the completion of open-ended tasks.