Nancy Bayley (28 September 1899 – 25 November 1994) was an American psychologist best known for her work on the Berkeley Growth Study and the subsequent Bayley Scales of Infant Development. Originally interested in teaching, she eventually gained interest in psychology, for which she went on to obtain her Ph.D. in from the University of Iowa in 1926. Within two years, Bayley had accepted a position at the Institute for Child Welfare (now called the Institute for Human Development) at the University of California, Berkeley. There she began the longitudinal Berkeley Growth Study, which worked to create a guide of physical and behavioral growth across development. Bayley also examined the development of cognitive and motor functions in children, leading to her belief that intelligence evolves