The children were on the cocoa plantation, in the market selling goods, at their family farms — anywhere, it seemed, but in Joseph W. Barber’s classroom. It was 2003, and Barber was in Ghana as part of the Peace Corps. He was teaching high school math and science, and he noticed that only about 60 percent of school-age children attended class. “These parents are doing something wrong,” Barber couldn’t help thinking. He started asking why. In doing so, he looked at the village …