In 1920, Piaget worked with Théodore Simon at the Alfred Binet Laboratory in Paris. Piaget evaluated the results of tests, put together by Simon, that were meant to measure child intelligence and draw connections between a child’s age and the nature of his errors. For Piaget, it raised new questions about the way that children learn. Piaget ultimately decided that the test itself couldn’t really be changed. In the revised version, he allowed children to explain the logic of their "incorrect" answers. In reading the children’s explanations, he realized that children’s power of reasoning was not flawed after all. In areas where children lacked life experience as a point of reference, they logically used their imagination to compensate. He additionally concluded that factual knowledge should not be compared with intelligence or understanding.
Before Piaget’s work, the common assumption in psychology was that children are merely less skilled thinkers than adults. Piaget showed that young children think in strikingly different ways compared to adults. Over the course of his six-decade career in child psychology, Piaget also identified four stages of mental development, called Schema.