Many online learning contexts are characterized by both high levels of student diversity on socio-demographic attributes (e.g., gender, first language) as well as task-related attributes (e.g., prior online-learning experiences, prior degrees). This longitudinal study investigated the relationships of multi-attributional diversity with CSCL processes and outcomes in a cohort of 1525 distance education freshmen randomly allocated to 343 groups over the course of a nine-week CSCL assignment. Group-level path analyses revealed that, if not explicitly managed, higher multi-attributional socio-demographic diversity was negatively related to the groups' structural integration (computed from digital data). Lower structural integration, in turn, was positively related to lower task-related collaboration time among students and, ultimately, a poorer grading of the groups' work by independent tutors. Moderation analyses further indicated that high task-related diversity operated as an amplifier of the negative relationship of high socio-demographic diversity with structural integration pointing to a risk constellation that requires active intervention.