When Kojo Muzala’s family were struggling to put food on the table in northern Ghana two years ago, an uncle brought the 15-year-old to the more prosperous south to work on a rubber plantation.

Kojo, now 17, is one of more than 70 million child labourers that the International Labour Organisation (ILO) says are active in Africa, many of them supporting large families or keeping key sectors of the economy going.

Child rights organisations take a tough line, saying the kids should be in school. Paradoxically, taking jobs is exactly how many of them pay their school fees. “I don’t like it, but I need it for my education,” Muzala said of his job. “I can’t afford to stay in school unless I do this work.”

Ghana, with a population of 30 million and exports of oil, gold and agricultural goods such as cocoa and rubber, is one of West Africa’s more successful economies, but poverty remains high.

In 2016 the U.N. children’s fund (UNICEF) estimated that 3.65 million Ghanaian children were living in poverty. Muzala usually works at weekends or early in the morning before school starts, and inevitably misses the odd school day.

“It’s very tiring,” he says. He earns 600 Ghana cedis — about $125 — a month, which is not a bad wage in rural Ghana. He sends half of that to his mother in the north, and the rest pays his fees and living expenses.