This study was driven by two primary objectives. The first objective focused on exploring the relationship between transformational and transactional leadership practices and teachers’ perceptions of their principals’ effectiveness. The second aimed to evaluate the adequacy of leadership training programs in Cyprus, with particular emphasis on how well these programs foster transformational leadership skills. To effectively address these goals, the research employed an explanatory sequential mixed methods design. For the quantitative phase, the Multifactor Leadership Questionnaire was administered to 630 teachers from 28 schools across all districts. Confirmatory Factor Analyses indicated that the Transformational and Transactional leadership dimensions could be represented by a higher-order factor. Subsequently, Structural Equation Modeling revealed a positive association between Transformational/Transactional leadership and principal effectiveness, whereas Passive-avoidant leadership showed a small negative association. For the qualitative phase, semi-structured interviews were conducted with five principals exhibiting different levels of adoption of transformational practices. Thematic analysis revealed shortcomings in current training programs, including a lack of substantive focus on preparing principals to become transformational school leaders. Overall, the study highlights the importance of transformational school leadership practices in shaping teachers’ perceptions of their principal effectiveness and emphasizes the need to revise principal training programs by incorporating transformational content.