The present study examined the impact of language TEACHERs’ gender, age, and experience on their self-efficacy. Moreover, it aimed to find out the mediating role of TEACHER education in modifying the effects of foregoing variables. To this end, a stratified sample of 180 English TEACHERs in high schools, private language institutes, and university settings in seven cities in Iran were initially handpicked as the participants of the study. Next, TEACHERs’ Sense of Efficacy Scale (Tschamen-Moran & Woolfolk-HoyHoy, 2001) was administered to the participants to specify their initial self-efficacy. Further, they attended a 20-session in-service TEACHER TRAINING program focused on theoretical and empirical issues related to learner variables and aiming at empowering the participants to tackle relevant problems in the context of the classroom. Finally, The Self-Efficacy Scale was administered to probe viable changes in the participants’ self-efficacy posterior to the treatment in relation to gender, age and experience. Results showed significantly higher levels of selfefficacy for males prior to and for females after the treatment. Additionally, the findings revealed that TEACHER self-efficacy was positively influenced by increase in TEACHERs’ age and teaching experience and that in-service TEACHER TRAINING could avert disparities among the TEACHERs across the diverse age groups and experience levels. The results underscore the paramount importance of in-service TRAINING courses aimed at empowering TEACHERs.