This paper is one of a series of Young Lives Project working papers, an innovative longitudinal study of childhood poverty in Ethiopia, India (Andhra Pradesh State), Peru and Vietnam. Between 2002 and 2015, some 2000 children in each country are being tracked and surveyed at 3-4 year intervals from when they are 1 until 14 years of age. In addition, 1000 older children in each country are being followed from when they are aged 8 years.