This is a longitudinal case study using a mixed-methods research design to track how two Korean university students improved their English writing competence over one year with the aid of automated writing evaluation (AWE) program, Criterion. The participants wrote essays outside of class every month for one year, submitting first and later second drafts. The participants completed a TOEIC writing test at the beginning and end of the study; students' reflections on their writing development, obtained through interviews and journal entries, were also examined. A comparison of scores, errors, and quantitative measures of fluency and grammatical complexity indicated writing improvement. Both participants used Criterion feedback effectively to render informed judgments and valid corrections. Essay revision based on Criterion feedback yielded more self-directed learning and greater comfort with writing in content courses. It is suggested that the effect of AWE feedback transfers to long-term improvement. The results point to the potential benefit of AWE use in individual out-of-class writing practices.