This study examines the guided use of ChatGPT in a higher education English for Specific Purposes (ESP) course for B2-level undergraduates in Information and Documentation. Over one semester, ChatGPT was integrated into a structured cycle of drafting, comparison, revision, and reflection rather than used as an unmediated text-generation tool. The classroom-based mixed-methods study drew on two core AI-supported writing activities, student-completed comparative analysis tables, and an end-of-course questionnaire including open-ended responses. Textual analysis focused on paired excerpts from students’ original writing and ChatGPT-supported revisions across grammar and syntax, vocabulary and register, textual cohesion, and clarity and precision. The examples show concrete within-task revisions, while students’ explanations indicate explicit attention to linguistic and textual changes. Questionnaire responses also point to positive perceptions of usefulness, motivation, autonomy, and prompt awareness. The findings provide context-specific evidence of revision awareness and engagement with guided AI-supported writing, but they should not be read as a standardised measure of longitudinal writing development. The study highlights the importance of teacher mediation, critical evaluation, responsible use, and AI literacy in disciplinary writing instruction.