This study primarily investigated the role of interactional factors in an unstructured face-to-face collaborative learning environment with challenging engineering activities. We explored dialogue patterns in terms of quality of interaction, students' scaffolding instances, and discourse moves for productive interactions of collaborative dyads in the context of the Interactive-Constructive-Active-Passive (ICAP) framework. The sample included 72 engineering students for the "interactive" and "constructive" conditions. Students' understanding of material science and engineering concepts were measured using pre and posttest design. Results showed students in the interactive condition performed significantly better than students in the constructive condition. Verbal analysis of approximately 12 hours video recordings and 210 pages of transcriptions for students' dialogue in the interactive condition indicated a strong relation between the quality of interaction, scaffolding instances, and individual learning gains. In addition, a verbal analysis examining each utterance based on the discourse moves revealed that the certain moves are significantly linked with learning outcomes.