In the present study cross-age peer tutoring was implemented in a higher education context. Fourth-year students (N=39) operated as online tutors to support freshmen in discussing cases and solving authentic problems. This study contributes to a better understanding of the supportive interventions of tutors in asynchronous discussion groups. Peer tutor interventions were studied by means of a content analysis scheme based on the e-moderating model of Salmon [Salmon, G. (2000). A model for CMC in education and training. E-moderating. The key to teaching and learning online. London: Kogan Page]. The descriptive results reveal that the type of tutor activities varies over the consecutive discussion themes. No evidence was however found for a significant evolution from introductory and social talk to contributions eliciting cognitive processing and critical thinking along the themes. Tutors' social support seems to be of continuous importance. Further, cluster analysis resulted in a classification of the tutors into three different subtypes or tutor styles ("motivators", "informers" and "knowledge constructors"), which was interpreted as confirmation of Tutor-dependent online peer tutoring behaviour.