This study examines the role of artificial intelligence (AI) as a reflective coach in graduate ESL practicums, using Activity Theory to assess its impact on student-teachers' (STs) reflective practices. An exploratory case study of 26 graduate ESL STs was conducted, with data from AI interactions and post-reflection questionnaires analysed qualitatively. Findings indicate that AI enhances STs' reflection, providing a structured, data-driven method for pedagogical development and personalised anytime feedback, thereby addressing feedback challenges in ESL teaching practicum courses. Despite limitations like diverse ST backgrounds and practicum environments, findings suggest AI's promise for transformative learning experiences. The study concludes that AI, as a reflective tool in ESL practicums, warrants further research into its impact on teacher development and adaptability in various teaching contexts.