["TESOL Quarterly, Volume 60, Issue 1, Page 218-260, March 2026. ", "\nAbstract\nThe current emphasis on core competencies in English education positions educators as key agents in curriculum transformation. However, research on teacher agency has predominantly centered on North American and European contexts, resulting in limited studies on primary and secondary education, particularly within China. This study aims to address this gap by examining the manifestations and influencing factors of high school English teachers' agency through an ecological lens. Adopting a qualitative case study approach, we investigated the agency of two English teachers through interviews, classroom observations, and documents. Thematic analysis revealed that although both teachers ideologically support and understand the new curriculum, their instructional practices do not fully reflect this congruence, indicating a “restricted teacher agency.” This discrepancy is attributed to variations in their past educational and professional experiences, current teaching environments, and short‐term goals, with personal, relational, and contextual dimensions of teacher agency emerging as primary influencing factors. This study concludes with theoretical and practical implications for English teachers, school administrators, and teacher educators.\n"]