This in-situ, causal-comparative study examined the difference in the quality of online discussions performed by learners with diversity in age and ethnicity status within different online interaction arrangements. Data was collected from 463 students in 19 online courses mainly via a content analysis with online interaction transcripts and an artifact analysis of online course sites and documents. The findings indicated a negative correlation between older adult students and online discussions of individualistic knowledge construction. The interaction arrangement prioritizing the student-to-student interaction reinforced knowledge-constructive online discussions. The interaction arrangement with a balanced requirement of student-to-content, student-to-instructor, and student-to-student interactions promoted reflective learning discussions. There is disciplinary effect on the interactivity and the amount of social and knowledge-sharing discussions. (Contains 7 tables.)