The rapid adoption of digital technologies in higher education has reshaped how students learn, collaborate, and engage, yet assumptions that online learning automatically enhances educational experiences remain largely unexamined. This study examined how students organised academic activities and appropriate digital tools within a fully online learning environment. Framed through a sociocultural perspective on mediated action, the study employed a qualitative case study design involving over 60 students and 30 hours of semi-structured in-depth interviews with ten university students. Findings revealed an underexplored pattern of structured but non-linear group work, in which students improvised coordination practices through WhatsApp, Padlet, voice notes, calls, and peer reference. First-come, first-served task allocation, volunteer compilation, and peer-based checking enabled students to organise group work but also contributed to uneven participation and limited opportunities for negotiation. Students further adapted their learning activities to home commitments, connectivity problems, and asynchronous communication, often prioritising task completion and submission over deeper content scrutiny. These findings demonstrate that student agency in online learning involves substantial coordination work, as learners construct and adapt social structures around available digital tools. However, such agency does not necessarily produce equitable or meaningful participation. The study contributes to sociocultural understandings of online learning by showing how students actively construct mediated collaborative practices when physical co-presence is absent, highlighting the need for pedagogical structures that support coordination, participation, and meaningful feedback.