Purpose: Despite occasional claims for the coexistence of transformational leadership and instructional leadership in schools, the literature is dominated by views supporting an "either/or" orientation. This is especially true in the wake of recent findings that instructional leadership has a greater impact on student learning. This study, going beyond simply evaluating whether these two modes of leadership complement or contradict each other, explores how they may intersect in complex and nuanced ways. Specifically, I examine the moderating effect of transformational leadership on the impact of instructional leadership on student outcomes. Research Design: A questionnaire, composed of items to measure instructional and transformational leadership, student outcomes, school background factors, and informant's demographic variables, was sent to the vice-principals in Hong Kong schools. Hierarchical regression analysis was used to factor out the effect of informants' personal and school factors on leadership perception and student outcomes in the testing of the moderating effect. Findings: With evidence drawn from 177 aided schools, this study confirms the moderating effect of transformational leadership through the identification of a disparity in the effect of instructional leadership on student outcomes corresponding to disparate levels of transformational leadership enactment in schools. Implications: The effect of instructional behaviors on student outcomes is considered to be situationally contingent on the extent of transformational behavior enactment. Despite its lack of a direct impact on student outcomes, transformational leadership serves as a necessary, although insufficient, condition for the effective implementation of instructional monitoring measures. Limitations of the study are also discussed.