This study presents an analysis of a MOOC on inquiry and technology for in-service teachers, which was designed to scaffold multi- ple disciplinary knowledge communities through common weekly themes, and course-long collaboration scripts happening at different social planes. Using our course design to inform the design of the analysis, we examine how the discourse in each semantically meaningful cohort (Special Inter- est Groups, SIGs) is indexed to the weekly themes, and develops these themes in areas informed by the discipline, and by the group dynamics. We show that SIG membership influences individual contributions, and that more cohesive disciplinary SIGs are correlated with higher quality student work.