In the late 1960s, researchers began doling out a nutritional supplement to families with young children in rural Guatemala. They were testing the assumption that providing enough protein in the first few years of life would reduce the incidence of stunted growth. It did. Children who got supplements grew 1 to 2 centimetres taller than those in a control group. But the benefits didn't stop there. The children who received added nutrition went on to score higher on reading and knowledge tests as adolescents, and when researchers returned in the early 2000s, women who had received the supplements in the first three years of life completed more years of schooling and men had higher incomes.
Since the Guatemalan research, studies around the world—in Brazil, Peru, Jamaica, the Philippines, Kenya and Zimbabwe—have all associated poor or stunted growth in young children with lower cognitive test scores and worse school achievement. A picture emerged that being too short early in life is a sign of adverse conditions—such as poor diet and regular bouts of diarrhoeal disease—and a predictor for intellectual deficits and mortality.