This chapter is aimed at beginners or practising principals who wish to reflect on leadership for social justice placed in the ecological and sustainable demands of today’s world. To this end, it uses fragments of interviews from a series of case studies in successful and unsuccessful secondary schools in disadvantaged contexts, following the methodology provided by the International Successful School Principalship Project (ISSPP). The interview extracts reflect the views of different members of successful and unsuccessful schools, which strive equally to improve the personal and academic lives of their students but which employ different approaches to leadership for social justice. The findings of the case studies capture the subtle contradictions involved in exercising a planet-friendly social justice leadership and offer an opportunity for principals in training to reflect on how to become successful leaders for social justice and sustainable development. Perceptions elicited by comparing the comments made by successful and unsuccessful principals under the same contextual conditions, but with different ways of dealing with problems, can help principals preparing to be leaders for social justice to develop the critical awareness necessary to be successful in this endeavour.