Successful school leadership in disadvantaged contexts is a topic of debate in the context of the Spanish education system. There needs to be clear identification of the concept of school success and what successful school leadership means. Thanks to the research carried out within the ISSPP project in Spain, we have been able to expand our knowledge on how success is defined in disadvantaged contexts: How have principals contributed to their school’s success? How has success grown and been sustained? And how have successful principals overcome internal and external factors to build a strong professional identity that enables them to fight for social justice? The ISSPP research in Spain finally concludes that the leadership variable may be considered decisive in the learning outcomes of pupils. It is not only the context variable that would be decisive in academic results, but rather leadership capable of making the moral purpose of education a reality.