Individual writing and collaborative writing skills are important for academic success, yet are poorly taught in K-12 classrooms. This study examines how sixth-grade students (n = 257) taught by two teachers used Google Docs to write and exchange feedback. We used longitudinal growth models to analyze a large number of student writing samples (n = 3,537) as they changed across individual writing sessions (n = 18,146), and multiple regression analyses to relate writing quantity and types of feedback to changes in students' standardized test scores. Additionally, student survey data and content analysis of students' writing samples were used to contextualize and interpret students' writing patterns. Overall, students had a positive attitude towards using Google Docs for editing and for the provision and receipt of feedback. They received various types of feedback from both their teachers and peers, but most were direct in character and in the areas of mechanics and grammar errors. However, neither students' writing quantity nor their types of feedback on Google Docs was associated with their writing achievement. Our findings suggest that cloud-based technology could be integrated into K-12 classrooms to support students' writing and editing, and to engage students in collaborative writing and improve interactions between writers and readers.