Nations throughout the world have been engaged in efforts to redefine the role of principals to include instructional leadership. This is based upon research that has verified a positive indirect relationship between principal instructional leadership and student learning. This study tested a moderated mediation model of how the power distance orientation of teachers influences the effects of principal instructional leadership on teacher agency and classroom instruction. Data collected from 464 teachers in 65 middle schools in Oman were analysed using structural equation modelling, factor analysis and bootsrapping. The results supported a partial mediation model in which principal instructional leadership was associated with moderate direct and indirect effects through teacher agency on classroom instruction. In addition, lower power distance in principal--teacher professional relationships was associated with stronger effects of instructional leadership on teacher agency. These findings support assertions that instructional leadership is a relational process rather than a top-down bureaucratic form of leadership.