This study investigated (1) the challenges encountered by a heterogeneous group of first year undergraduates during a synchronous on-line collaborative writing activity conducted through Google Classroom using Google Docs and (2) their perceptions of the pedagogical approach. Five sub-groups of undergraduates participated in the study, and their written transcripts were analysed for patterns of interaction in terms of equality and mutuality based on the Taxonomy of Writing Change Functions and Scaffolding Strategies (Li and Zhu, 2017). Data on learner perceptions were analysed for underlying themes. The findings, which were interpreted from the perspective of the Complex Dynamic Systems Theory, revealed that synchronous on-line collaboration is complex and challenging due to the dynamic patterns of interaction. This study concludes that Google Docs is a useful pedagogical tool and could be used for second language writing development despite the challenges. However, in transferring the findings to other second language learners or learning contexts, caution needs to be applied.