The Lesson Study approach, a subdivision of inquiry-based instruction, is majorly centered on teachers’ professional development through requiring them to act as classroom researchers. This approach has become popular in various academic environments and holds a promising potential as a gateway to teachers’ career advancement. EAP instruction, however, differs from general EFL instruction in that it is designed to meet university students’ academic needs (Hyland, 2006). This study, accordingly, applies the Lesson Study approach, with the aim of providing an improved comprehension on the ways educator growth is made via social setting and team-teaching among instructors when participating in research initiative; it also investigates the ways such learning results in changes to instructors' perceptions on the model itself as well as the consequent teaching alterations. Five Iranian EAP instructors participated in a 12-week Lesson Study program. The data were collected through pre- and post-interviews, reflective journal writings, and field notes from the researcher to assess the effect of the program on their professional development. Findings imply that the instructors' perceptions regarding practice were favorable both before and after the study. Working through a Lesson Study process satisfied their EAP demands and helped them learn more and gain a better understanding of how to teach more efficiently and improve their perceptions of teaching. They also believed that the approach greatly contributed to their EAP professional and personal development. The findings indicate the importance of peer collaboration in fostering reflective teaching and improving instructional methods, leading to better student learning outcomes.