On definitional and conceptual basis, strong correspondences exist between leadership and the teaching profession yet leadership is nonetheless occasionally studied in the classroom context. This study investigated in-class teacher leadership based on the Full Range Leadership (FRL) model in tertiary-level English language teaching context in Turkey, with the aim of eventually identifying the effective/ineffective classroom leader characteristics. This paper reports the results of a study designed with a mixed methods approach, using a questionnaire survey, which included Classroom Leadership Instrument, a modified version of Multifactor Leadership Questionnaire administered to the students and face-to-face interviews with both instructors and students. One particular subject course was determined in two English language-related departments in a Turkish state university and the instructors teaching and the students taking this course were selected as the subject group of the study. 305 students took part in the survey while among these students, 18 were further interviewed besides the four instructors teaching the course. Quantitative data were analyzed through descriptive tests while interviews and observations were content-analyzed. Both quantitative and qualitative results, in broad terms, showed that language instructors displayed all three leadership styles of FRL, namely, transformational, transactional and laissez-faire leadership, with changing extents for each style. The results indicated that instructors with higher tendencies for transformational and active components of transactional styles were rather more organized, enthusiastic and committed and they were attributed with more positive and effective characteristics by their students while those with higher passive transactional and laissez-faire leadership scores were accordingly less effective in both teaching activities and their relationships with the students. Lastly, it is concluded that transformational and active transactional leadership characteristics contribute to effective leadership inside the classroom and an integration of these characteristics into teaching practices and teacher-student interaction promises potential positive outcomes.