Aichetou, a 14-year-old girl, lives on the outskirts of Nouakchott, the capital of Mauritania, in Africa’s Sahel region. Every day, she makes a difficult trek through the sand to get to a school with no drinking water or sanitation, where she barely learns, owing to a lack of textbooks and trained teachers. And she is not alone: tens of millions of schoolchildren worldwide face similar circumstances, while 262 million children and youth are not in school at all.