Jean Piaget was a psychologist who studied cognitive development. Piaget's theory on cognitive development mentions that all children, regardless of socio-economic factors, go through a series of stages throughout their early life. He notes that each of these four stages is different from the others in terms of the quantity and quality of information and knowledge gained. He goes on to note that children are not capable of completing certain tasks or understanding concepts and ideas until they reach the stage in their cognitive development that will allow them to complete that task or understand a particular concept and idea. A child is able to advance from one stage to another once that child has the experience and knowledge required to advance.
The four stages of Piaget's Theory of Cognitive Development are the following: sensorimotor, preoperational, concrete operational, and formal operations. In general, a child goes through the first three stages on or before age 11 and the stage of formal operations goes on to adolescent years.