Extramural English (EE) with teacher support may work more effectively for Asian EFL learners' willingness to communicate in a second language (L2 WTC) given their sociocultural and educational contexts. Therefore, a teacher-supported EE program was developed to help students transit from teacher-controlled to learner-driven EE activites. Ninety Chinese EFL university students were randomly assigned to three groups: EE (n = 30), teacher-supported EE (n = 30), and conventional class (n = 30). Pre-post (trait-like WTC) and real-time survey (state-like WTC) results showed that the teacher-supported EE group outperformed the other groups in improving their L2 WTC. Interviews (n = 20) identified five factors that influenced the enhancement of their L2 WTC: emotional support from peers and teachers, teachers’ cognitive and pedagogical support, a low affective filter, increased topical knowledge, and increased English lexical knowledge. This study is the first to demonstrate that (a) EE activities contribute to improvements in both trait-like and state-like L2 WTC levels in EFL learners, and that (b) the effectiveness of the EE program is enhanced when teacher support is provided, particularly for Asian EFL learners.