Building effective and supportive communities of practice in an asynchronous environment can enable students to learn from each other at their own convenient times without the need to meet for discussing concepts. In an undergraduate course with a large amount of content to learn, working collaboratively to answer practice exam questions can help encourage deeper learning and understanding. This project examined whether exam performance can be positively influenced by online collaboration during revision and suggests that the quality of an individual's contribution has a direct effect on his/her subsequent exam performance. We compared two student cohorts' exam marks from their previous 3 years of exams with how they performed in Year 4 after using PeerWise (an online repository of multiple-choice questions that are created, answered, rated and discussed by students). In addition, we looked at the quantity and quality of their contribution in PeerWise to evaluate how this affected their fourth year exam performance. We confirmed that exam performance is improved by authoring questions in PeerWise, but found it is further enhanced by replying to, and commenting on, others' posts as well.