There is a great contemporary interest in improving schools in disadvantaged contexts, specifically, in Spain it is a topic of concern and debate. School leadership is considered a decisive variable for improvement and school success, but it is also considered necessary to identify the concept of school success and what successful school leadership means in disadvantaged contexts. Thanks to the research carried out in Spain within the International Successful School Principalship Project (ISSPP), it has 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 advantaged/disadvantaged context variable that would be decisive in academic results, but rather leadership capable of making the moral purpose of education a reality.