This study examined the relationship between discussion forum contributions and course assessment results in a statistics MOOC. An important feature of the study is that it distinguished between discussions that were related to the learning of course material (“content-related”) and those which were not (“non-content”). Another contribution is that the study evaluated the additional usefulness of social centrality measures in predicting course grade after the quantity of forum contributions has been accounted for. Results showed that, overall, 15% of course learners contributed to the forums and these learners had a significantly higher rate of successfully passing the course than non-contributors (64% vs 32% passing). Learners who made posts to both content-related and non-content threads had a higher passing rate than those who only contributed to one type or the other. Among learners who successfully passed the course, there were no differences in course grade when comparing discussion contributors and non-contributors overall; however those who contributed to content-related threads performed slightly better than those who did not (course grade of 87% vs 85%). A predictive model based on the number of posts made to content-related threads explained a small proportion of variance in course grades; addition of social centrality measures did not significantly improve the variance explained by the model.