Respect Ruvimbo Topodzi was 15 and walking home from school in her native Zimbabwe when a 22-year-old man asked her out. She turned him down but it was too late. Her father saw them and assumed they were already together. He told her she had to marry the man and live with him. She dropped out of school and soon became pregnant.

It was only when her husband became abusive that she was allowed back to the family home. Since then, Topodzi has been working to stop other girls having the same experience.

She took on the government to change the law and increase the minimum legal age of consent for marriage from 16 to 18. “As a mother and survivor of child marriage, I am so passionate about ending child marriage,” she told AFP at a recent conference on the subject in Ghana’s capital Accra.

“I know how it feels to be married early and I know how you handle things in your marriage—that is so difficult.” According to a new World Bank report, more than a third of girls in sub-Saharan Africa marry before their 18th birthday, which costs countries billions of dollars in lost earnings.

Estimates for 12 countries suggest some $63 billion (55.5 billion euros) is lost because child brides complete fewer years of formal education than their peers who marry later.