There are a number of challenges and debates surrounding the implementation of mental health interventions in schools. These include recognising the complexity of influencing factors and the interdependency of key components; the critical importance of monitoring school-based implementation in particular contexts; employing multimethod evaluation designs that can capture the complexity; and judging success using mental health and educational outcomes. These factors are shaped by both mental health and educational research. The prevention paradox focusing on the whole population ‘prevents’ more illness than targeting programs to specific individuals, and is exemplified in school mental health promotion that utilises an ecological or whole school approach. MindMatters, an innovative Australian mental health promotion and pr evention program, illustrates the challenges in this new field of endeavour. Its design and implementation are consistent with recommended effective practice, a comprehensive program that targets multiple health outcomes in the context of a coordinated whole school approach (Jané-Lopis, Barry, Hosman, & Patel, 2005). MindMatters moves beyond the sole focus on the curriculum to acknowledge the key roles of teacher professional development and whole school change within a strengths-based approach. As recommended by Jané-Lopis et al. (2005) measures of key school mental health outcomes are being used, ranging from absenteeism and drop-out rates to the development of social skills and academic achievement. The MindMatters evaluation suite of five separate yet interrelated evaluation studies illustrates some of the complexity involved.