<![CDATA[Generative artificial intelligence is increasingly integrated into English language learning, yet empirical evidence on its effectiveness for improving grammatical accuracy among Indonesian senior high school EFL learners remains limited; most existing studies have focused on university students or on general perceptions rather than on grammatical accuracy as a specific, measurable outcome. This gap motivated the present study, which investigated the effectiveness of ChatGPT-assisted feedback in improving eleventh-grade students' grammatical accuracy in writing and explored their learning experiences during AI-assisted revision. Grammatical accuracy was selected as the primary outcome because it is one of the most persistent and measurable challenges in EFL writing and underlies clear written communication. An embedded mixed-methods design combined a quasi-experimental pre-test-post-test control-group design with a questionnaire and semi-structured interviews. Sixty-six eleventh-grade students at SMAN 2 Parepare participated; the experimental group (n = 33) received ChatGPT-assisted feedback across four writing-revision sessions, while the control group (n = 33) received conventional classroom feedback. The experimental group significantly outperformed the control group on the independent post-test (t(64) = 5.69, p < .001, Cohen's d = 1.40), and questionnaire and interview findings indicated that ChatGPT-assisted feedback enhanced grammar awareness, writing improvement, motivation, and revision behaviour, while also encouraging critical evaluation of AI-generated suggestions rather than passive acceptance. These findings suggest that ChatGPT is an effective supplementary formative-feedback tool for developing grammatical accuracy rather than a replacement for teacher-led instruction. For EFL teachers, the results indicate that structured, teacher-mediated AI feedback can be integrated into writing classes without displacing the teacher's pedagogical role. The study contributes empirical evidence for embedding structured AI-assisted feedback into EFL writing pedagogy at the secondary level, and offers a replicable model for classrooms facing large enrolments and limited time for individualized correction.]]>
