Grounded on cognitive elaboration theory, this study aims to investigate how students' dyadic conceptual elaboration changed with different group compositions, namely presence/absence of instructor and unfamiliar students in online asynchronous discussion. Adopting a repeated measure experimental design, data were collected from third-year students from two universities attending a "Fundamentals of Distance Education" course. Through a free learning management system, asynchronous discussions with five different group compositions were held for six weeks. The transcripts of the online discussions were coded using thematic units. The data were analyzed using the Kruskal-Wallis H tests and Mann-Whitney U tests. The findings indicated that group compositions significantly affected students' dyadic conceptual elaboration. The findings also revealed that increasing group heterogeneity was critical for students to generate new, valuable, and creative ideas. The study concludes the inclusion of instructors and unfamiliar learners in online asynchronous discussions for an enhanced dyadic conceptual elaboration.