Background study: Although the number of computer-based instruction has increased drastically, the understanding of how design features of learning modality can affect learning remains incomplete. This partly stems from studies' heavy focus on modified output. Therefore, how interactive nature of computer-mediated learning feeds into learning is under examined. Objectives: This study examined the potentials of multimodal and text-based computer-mediated communication (CMC) to support learner communication repair, co-regulation patterns and engagement dimensions. Method: To this end, collaborative online writing performance of 30 English as a Foreign Language learners in Moodle and online writing forum was analysed via conversation analysis. Data from stored conversation of Moodle and chat logs of writing forum were coded for communication repair to trace language related episodes (LREs), co-regulation patterns and students' engagement dimensions. Results: The frequency analysis of coded data on LREs indicated while multimodal CMC involved students in global and organisational and content LREs, text-based computer-mediate communication involved students in morphosyntactic and lexical LREs. Results also indicated significant differences in co-regulation patterns in multimodal and text-based computer-mediated communication. While students enacted planning, monitoring co-regulation practices in multimodal computer-mediated communication, students in text-based CMC executed evaluation and elaboration co-regulation practices. Findings also indicated that students were differentially engaged in learning. Students were more emotionally and socially engaged in multimodal CMC and cognitively and behaviourally engaged in text-based computer-mediated writing. Conclusions: The results posit dual function for CMCs, as a mean for communication and cognitive co-regulation. However, dynamics of interaction is influenced by the mode of interaction.