Our study contributes to the research on computer-mediated communication in higher education by experimenting a modern communication tool called Slack. In particular, we consider using Slack to support students’ peer interactions during Master’s thesis work. For this purpose, we designed a case study that was executed in a Master’s thesis seminar course. During the course, all out-of-class communication was carried out by using Slack, instead of e-mails or learning management systems. After the course, we used a questionnaire to investigate how the students perceived Slack for asking for assistance, their intention to use Slack, and Slack’s ease of use. Furthermore, the questionnaire asked feedback about challenges that the students found in slack. To examine the students’ peer support in Slack, we analysed the messages in the course’s public discussion channels. We investigated opportunities and challenges of Slack from instructional perspective by conducting an auto-ethnographic data collection. Our analysis revealed that the students perceived Slack as an easy-to-use communication tool with a low threshold of asking questions. The students also expressed high intentions to use Slack in the future. However, the students were worried of information overload in Slack, frustrated with decentralisation of communication tools in higher education, and cautious of using communication tools that are not officially supported by the university. The students’ interactions were assigned to three categories: practical, technical, and thesis-related. Analysis of these categories revealed that the students were able to explicate and solve issues in Slack, but the issues were only related to practical and technical problems, instead of actual Master’s thesis writing. The teacher perceived that Slack enhanced bi-directional communication with the students, but faced issues related to file management and user authentication. The results implicate that developing an alternative for Slack from educational premises could be more useful than a product that is not originally developed for pedagogical needs. Finally, we present recommendations that help educators to use Slack in their educational practices.