This longitudinal case study examined middle school students' (N=102) in-class digital literacy practices using Google Docs and their subsequent learning outcomes and perceptions in a technology-supportive K-8 school. Despite the widespread use of synchronous technology in writing, little research has been conducted on students' collaboration practices and their impacts on text outcomes and perceived learning, particularly among linguistically diverse students. Using a mixed-methods approach that combines qualitative, quantitative, and text mining methods, I examined multiple aspects of synchronous collaborative writing (e.g., patterns, strategies, phases, textual outcomes, perceptions of group writing) over the course of an academic year. I also discussed the implications of the new digital literacy practices for teaching and learning in K-12 academic settings. In my three-part dissertation, triangulation of multiple sources of data and analytic approaches revealed several major findings regarding the practices (Part 1), outcomes (Part 2), and perceptions (Part 3) of synchronous collaborative writing.First, the groups' collaborative writing practices (i.e., balance of written participation, editing amount, the use of collaborative writing strategies) tended to differ across the two key contextual factors: ability-grouping status and task types. Compared to the same ability groups, mixed-ability groups demonstrated patterns of unbalanced participation (e.g., frequent use of main writer strategy) with higher numbers of self-edits. This implies that students in mixed-ability groups may encounter difficulty in dividing work equally due to the writing proficiency gaps among members (i.e., higher imbalance).Second, qualitative analysis of the focal groups' writing processes revealed distinct characteristics of collaborative and non-collaborative groups, and how such patterns shape group's subsequent choice of writing strategies. Of particular importance was the role of leadership in interaction patterns: unlike the non-collaborative groups (authoritarian/passive, dominant/withdrawn) characterized by dominant leadership, the groups with a collaborative stance (collectively contributing/ mutually supportive pattern, expert/novice pattern) involved distributed and fluid leadership that leveraged the opportunities for synchronous interaction.Third, I examined how multiple indicators of collaborative writing practices (e.g., participation evenness, editing amount, collaborative writing strategy) may relate to the quality of group text outcomes. Results re-confirmed the critical role of task types in collaborative writing. For example, in the narrative task involving a creative open-ended prompt, balanced participation and more number of co-authors tended to weaken the organizational aspect. However, no such effects were found in the argumentative and informative tasks characterized by more formal, closed genre structures.Fourth, I examined the phases of focal groups' community building (i.e., initial, conflict, intimacy and work, and termination phases) during their year-long engagement with collaborative group work. Qualitative analysis of multiple sources of data suggested that there were unique group tasks that needed to be accomplished in each phase, and the degree to which members effectively accomplished these sub-tasks ultimately determined the level of collaboration and perceived learning. The results also suggested that the intimacy and work phase --- during which members build trust, negotiate differences, establish membership, and pool resources---was particularly important for novice members' transition from peripheral to full participation.Fifth, I examined the perceived affordances and challenges of integrating synchronous technology in teaching and learning writing, as well as the contextual factors that shaped students' year-long engagement with the digital literacy practices. Several themes have emerged regarding the affordances (e.g., multiple entry points for participation, apprenticeship for 21st century literacy skills, support system for struggling writers), as well as the challenges (i.e., efficiency over quality, tension between collective vs. individual ownership) of engaging with the newly emerging digital literacy practices. The critical role of implementation contexts (e.g., technology-supportive instructional context, school's emphasis on collaboration and diversity, curricular integration and teacher's role) was also highlighted.Lastly, I discussed the theoretical, pedagogical, and methodological implications of the multiple findings. Theoretically, this study helps us explore the value of synchronous collaborative writing as a new literacies practice and also as a community practice, both of which may effectively bridge the gap between traditional in-class literacy practices and increasingly multimodal, out-of-school literacy practices. Pedagogically, the results provided strong implications for task design and implementation by investigating the under-examined impact of multiple factors (e.g., task types, ability grouping, interaction patterns) on students' collaboration practices and learning outcomes. Methodologically, this study demonstrated how the integration of a text mining approach may enhance the research capacity for understanding the multiple aspects of the emerging digital literacy practices, particularly when combined with qualitative investigations. Overall, the findings help us better understand how to integrate collaborative digital literacy in K-12 settings and how to maximize the educational affordances of synchronous technology to equip students with the essential writing skills for the 21st century. (Abstract shortened by ProQuest.).