Since the early 1980s, there have been universal calls for work in educational administration and, in particular, work on the leadership role of the principal (Murphy & Hallinger, 1992). In addition, the positive correlation that has been established between effective schools and effective principals (Brant, 1987) precipitated the need for further studies on the leadership practices of school principals at the various levels of the educational system. In a review of the literature on principal leadership and school effectiveness, Murphy and Hallinger (1992) found that studies during the preceding 15 years, conducted in 12 countries, focused mainly on principals of elementary schools and on principals of traditional secondary schools. However, because of the tremendous diversity with respect to how children are schooled, and the limited research in educational administration highlighting the contextual differences in schooling practices, there seems to be an urgent need to study school leadership in all settings. This paper therefore, attempts to investigate the extent of: (a) the use of principals' leadership; (b) the effectiveness of principals'Â leadership, and (c) the impact of the use and effectiveness of principals' leadership on (i) teachers' commitment and (ii) students' academic achievement in junior secondary schools in Trinidad and Tobago.