Adapting face-to-face (FTF) pedagogies to online settings raises boundary questions about the contextual conditions in which the same instructional method stimulates different outcomes. We address this issue by examining FTF and computer-mediated communication (CMC) versions of constructive controversy, a cooperative learning procedure involving dialogic argumentation and the shared goal of reaching an integrative position. One hundred seventy-one undergraduates were randomly assigned to a 3 (synchronicity: FTF, synchronous CMC, asynchronous CMC) × 3 (belongingness: acceptance, mild rejection, control) quasi-experimental design. As predicted, FTF and synchronous CMC conditions increased cooperation, epistemic conflict regulation, motivation (interest-value), and achievement (completion rate, integrative statements), whereas asynchronous CMC increased competition and relational conflict regulation and decreased motivation and achievement. Also as predicted, satisfying belongingness needs (through acceptance) increased cooperation, epistemic conflict regulation, and motivation compared with control. Unexpectedly, there was no evidence that mild rejection diminished outcomes. Results inform theory by demonstrating that FTF and CMC synchronicity represent boundary conditions in which constructive controversy stimulates different social-psychological processes and, in turn, different outcomes. Results also inform practice by showing that synchronicity and belongingness have additive effects on constructive controversy and that satisfying belongingness needs buffers but does not offset the deleterious effects of asynchronous CMC.