The scale of the global learning crisis is difficult to exaggerate. A recent analysis of international and regional assessments estimated that at least two-thirds of the world’s young people fail to acquire the basic skills needed to participate effectively in a modern economy. In affluent countries, roughly one child in four falls short. In low-income regions, the proportion is far higher. Published calculations estimate that broad improvements in children’s academic development could add more than US$700 trillion to the world economy by 2100. 

The standard response is to demand better schools: more competent teachers, stronger curricula, greater accountability, higher standards, and longer school days or more years of education. All of these may help, but they begin too late for many children. The comforting assumption that schools can compensate for almost any earlier disadvantage is false in many cases; a child whose prenatal and early development is plagued by poor nutrition and health will often have a reduced capacity to later benefit from schooling.

Our research examined a biological record of those early conditions: the average difference in adult height between men and women. Across countries, populations in which the average height between the sexes is greater (that is, greater sexual height dimorphism) tend to perform better on international measures of academic achievement, at least up to a point. This relationship suggests that poor prenatal and early-childhood conditions can suppress not only physical development but also the capacity to profit from schooling.