Private schools in the United Kingdom are affordable only to those on the highest incomes. But surprisingly to many, this is not true across developing countries, where low-cost private schools are ubiquitous and affordable to all.

For nearly two decades I’ve been researching this phenomenon. I’ve visited low-cost private schools in more than 20 countries, from the vibrant slums of sub-Saharan Africa and South Asia to remote mountain villages in South-east Asia and the gang-dominated barrios of Central and Latin America.