This article examines the impact of the introduction of roles and the added value of self-assessment on students' level of knowledge construction in online asynchronous discussions in a first-year university course in instructional sciences. Students' postings in 20 discussion groups were used as the research data for this study. All messages, submitted during the 12-week discussion period and comprising four discussion themes of 3 weeks each, were analysed. Repeated-measures multilevel modeling was adopted to analyse the data from the content analysis. The results point at a significant positive impact of assigning roles to students. However, this positive impact depends on the moment of the introduction of the roles. Higher levels of social knowledge construction were found in discussion groups where roles were introduced right at the start of the discussions and faded out towards the end. The results further indicate that self-assessment has no significant added value.