Department heads are increasingly responsible for instructional leadership. Therefore, it is important to understand the antecedents of self-efficacy in their work, which can motivate them to increase their leadership efforts. Our theoretical model depends on principals' feedback for department heads, department heads' trust in their principals, and perceptions of time pressure. We argue that the relational trust between department heads and principals creates social exchanges that catalyze department heads' self-efficacy in instructional leadership, perceived job autonomy, and perceived role clarity. We explored our theoretical model using structural equation modeling of cross-sectional survey data completed anonymously by department heads. We found that effective feedback-based school leadership is positively related to department heads' self-efficacy and perceptions of job autonomy and role clarity, with relational trust between the principal and department heads playing a key role. Time pressure is also positively associated with department heads' mentoring self-efficacy. This study fills a gap in the literature and contributes to the field of leadership in learning by explaining the various antecedents to department heads' self-efficacy, perceived job autonomy, and role clarity.