Jean Piaget was a child psychologist, professor, author, and biologist. Though he had many academic interests, his primary focus was the child psyche. He did a lot of research in the area of child psychology and his conclusion is what is known as Piaget's Stages of Mental Development. He recognizes four main stages in a child's life: The Sensorymotor Stage (ages: birth to two), The Preoperational Stage (ages: 2-7), The Concrete Operational Stage (ages: 7-12), and The Formal Operational Stage (ages: 12-15). The Sensorymotor Stage , says Piaget, is when infants and babies are more concerned with learning about the physical world, objects, and their own physical development. The Preoperational Stage is when a child is learning and developing verbal skills, including reading and writing. The Concrete Operational Stage is when a child is beginning to understand abstract concepts, such as numbers and relationships. And, finally, The Formal Operational Stage is w...