The Writing Pal (W-Pal) is a novel intelligent tutoring system (ITS) that offers writing strategy instruction, game-based practice, essay writing practice, and formative feedback to developing writers. Compared to more tractable and constrained learning domains for ITS, writing is an ill-defined domain because the features of effective writing are difficult to quantify and individual writers can employ diverse strategies to achieve similar goals. The development of an ITS in an ill-defined domain presents particular challenges regarding comprehensive instruction, modularized content, extended practice, and formative feedback. In this article, we describe how the development of W-Pal has uniquely addressed these concerns and present the results of a study assessing the feasibility of this system in high school English classrooms. This study included 2 teachers and their 141 10th grade English class students who utilized W-Pal over a 6-month period during the academic year. Log-file analyses showed that students used all aspects of W-Pal, but activity and engagement was uneven throughout the year and decreased over time. Essay scores improved over time and surveys indicated that students perceived the lessons, games, and feedback as beneficial. However, specific aspects of the learning environment were critiqued as annoying, challenging, or lacking specificity. Overall, the results suggest that the system was generally well-received by the students but also offer insights for the development of ITSs in ill-defined domains.