An estimated "100-year gap" persists between education levels in developed and developing countries, and if business proceeds as usual in the education sector, this gap is not projected to close. Today, 250 million children around the globe--many of them having spent at least four years of school in a developing country--lack the most basic literacy and numeracy skills. Additionally, countries around the world are struggling to help young people develop 21st-century skills, such as critical thinking and collaborative problem solving, which are increasingly demanded by the labor market. "Millions Learning" tells the story of where and how quality education has scaled in the developing world. The story emerges from wide-ranging research on scaling and learning, including 14 in-depth case studies, from Brazil and Honduras, to Uganda and Zambia, to Jordan and India.

What we found is that from the slums of New Delhi to the rainforest in Brazil, transformational change in children's learning is happening at large scale in many places around the world. We found that successful scaling of quality learning often occurs when new approaches and ideas are allowed to develop and grow on the margins and then spread to reach many more children and youth. What constitutes the margins varies on a case-by-case basis. For some, it means a flexible central government giving freedom to its officials within a district to try a new approach. For others, it involves a community movement that develops new ways of reaching marginalized children whose educational options are limited.

Scaling from the margins occurs in two main ways: idea adoption, namely the spread of new approaches across an education ecosystem, and delivery innovation, the development of new ways to deliver education to marginalized children and youth. With the former, effective new approaches to improving components of the teaching and learning process--from curriculum, to materials, to teacher development--have spread across education ecosystems and been adopted by different actors. With the latter, new education delivery approaches for the most marginalized communities--such as distance learning models or alternative education programs--have developed and grown within and across countries. We identified 14 core ingredients, in different combinations depending on the context, contribute to scaling quality learning. Each of these ingredients is central for scaling effective approaches that improve learning. Their importance is frequently reinforced from evidence in the broader scaling literature. They include essential elements for designing, delivering, financing, and enabling scaling of quality education