In recent years, material development in English language teaching has received growing attention, yet the interaction between English language teachers and prescribed teaching materials remains an under-researched area. This study aims to address this issue and contribute to the understanding of teachers’ agency in their interactions with prescribed textbooks. The study addresses this gap by exploring how five high school English teachers in two major cities in southern and southwestern China interact with prescribed textbooks within the curriculum policy context. Through in-depth semi-structured interviews and documentary analysis, the study investigates teachers’ evaluation, adaptation, and exploitation of materials, revealing that while teachers exercise agency in material development, both textbook structure and external factors contribute to the deprofessionalisation of teachers. The findings underscore the complex relationship between a standardised curriculum and teachers’ context-sensitive practices, highlighting the need for flexible textbook designs and more supportive administrative practices to better facilitate teacher agency in classroom material use.