|Jean Piaget grew up in a tumultuous household with his father--a professor of history--and his mentally ill mother. He was a precocious child. One of Jean's first interests was nature, and he published several papers in his teen years on birds and mollusks. After he earned a Ph.D. in natural history from the University of Neuchatel in 1908, his interests turned to psychology, and he made began a career in the field of cognitive development. In 1921 he was named director of research at Jean-Jacques Rousseau Institute in Geneva. He was also on the faculty of the Sorbonne and the University of Geneva, and over the course of his career he was associated with many universities in Europe and America. After conducting an inquiry into the underlying causes of "mistakes" that children made on intelligent tests, Piaget spent a lifetime observing children, and arrived at a theory of development consisting of four stages of psychological growth. He was a prolific author, turning out a prodigious body of work, both books and research reports. Piaget's work is important to educators as well as to psychologists. Among the subjects he observed in developing his theories were his own children. Jean Piaget never had any formal training in psychology but he is, after Freud, perhaps the most cited author in the field.