This textbook is written after a robust research done on school effectiveness and school improvement in slums of Nairobi in Kenya. The research was based on a PhD study which the author submitted to the School of Education at the University of Birmingham in the UK as part of the requirements for the fulfilment of the award of the PhD degree in International Educational Management and Policy Studies in 2004. Since then the author has utilized his teaching and leadership experience in public universities in Kenya to update this study. Furthermore, this study helped the author as the lead expert in developing an Executive Master of Education (EMEd.) degree in leadership and policy -a professional tailor-made course for training secondary and college principals. The author identified the City of Nairobi as a one of the contextual realities in which schools in developing countries exist. This textbook provides readers with information useful to their schools which exist in different contextual realities of effectiveness and improvement.