Gesell, Arnold Lucius << guh ZEHL, AHR nuhld LOO shuhs >> (1880-1961), an American psychologist, became known for his studies of the behavior of infants and children. He found that the growing child’s behavior seemed to follow a set developmental pattern. He detected and described features of children’s behavior at different ages. His ideas are widely applied in child guidance and parental education. Gesell wrote Atlas of Infant Behavior (1934). He was born on June 12, 1880, in Alma, Wisconsin.