Throughout childhood, children undergo vast intellectual development that occurs in somewhat predictable stages. Jean Piaget, a developmental biologist who lived from 1896-1980, believed that these stages of psychological maturity affected a child's understanding. Piaget studied intellectual development in children through observation, talking and listening, and came up with four unique stages based on developments in brain growth throughout childhood.
Sensorimotor Stage (0-24 months)
From birth to 24 months of age, children undergo rapid physical and intellectual growth. During this stage, a baby develops from repeating actions to produce a desired result at four to eight months, to discovering new ways to produce a consequence at 12 to 18 months. As children in the sensorimotor stage continue to develop, they acquire the idea of "object permanence," meaning that they realise that an object can still exist even when it is removed from sight.
Preoperational Stage (2-7 years)
Children in the early preoperational stage, from 2 to 4 years of age, are egocentric, meaning that it is hard to understand another person's perspective. During these years children begin to grasp the concept of time, referring to the past as "yesterday" and the future as "tomorrow." By four years of age, most children can tell simple stories and are beginning to become more social and less egocentric. Language development during this stage is rapid and by the time a child is five years old, his vocabulary will likely include several thousand words. Additionally, he should be able to recognise simple printed words. By the age of six or seven, children generally begin to read and are able to represent objects with images and words. Although classification of objects occurs during the preoperational stage, it is usually done using only one feature, such as sorting coins into big coins and little coins.
Concrete Operational Stage (7-11 years)
During the concrete operational stage, children can not only understand another person's perspective, but multiple points of view. The thought process of a child in this stage becomes increasingly organised and logical, and he is able to reason and problem-solve with concrete objects. From age seven, children can follow simple rules and can classify objects by more than one feature.
Formal Operational Stage (11 years and older)
During the formal operational stage thinking becomes less concrete and more abstract. A child in this stage is able to think logically about the future and is able to consider hypothetical situations with a range of potential outcomes. Problem-solving during this stage is done systematically using predictions, which are revised when new learning occurs.