This longitudinal study serves as a model for examining and understanding the role of editing and its contributing factors in writing center tutorials. The study quantifies the frequency of and time devoted to editing in over 4,000 writing center tutorials and finds these quantities differ in statistically significant ways when broken down by user groups (gender, student standing, course level, and primary language); tutoring modes (face-to-face, synchronous-online, and asynchronous); and time of student visit relative to project due date. Analysis identifies contributing factors that influence frequency of and time spent on editing in tutorials by these groups, including group membership and their associated editing practices and tutorial habits. The study's findings fill an important gap in our understanding of what takes place in writing center tutorials and have significant implications for tutor training and marketing of writing center services.