Early in his career, Piaget went to work for Theodore Simon in Paris. Simon, along with Alfred Binet, was the author of the Binet-Simon intelligence test, the first successful test of its kind. Piaget’s job was to record the answers of five- to eight-year-old children in order to determine expected scores for each age group. Although he was hired to record the correct answers, he became far more interested in the children’s mistakes, in the typical patterns of error at each age. This sparked his interest in the development of children’s intellectual understanding of the world around them. He had found his life’s work. For the next sixty years, Piaget studied children’s behavior in great detail. From this data, he generated a voluminous body of writings on the subject and changed the way we look at intellectual development.