Cognitive development refers to "...how a person perceives, thinks, and gains an understanding of his or her world through the interaction and influence of genetic and learned factors" (Plotnik, 1999)

Jean Piaget was a psychologist who believed there are stages of cognitive development that each person must go through. Although there are ages connected with each stage, each person may reach these cognitive milestones at different rates.

The first stage is the Sensorimotor stage. This stage typically ranges from birth to 2 years. In this stage, children experience the world through the senses. During this stage, object permanence and stranger anxiety develop.

The second stage is the Preoperational stage. The age range for this stage is typically 2 to 7 years. In this stage, children are able to represent objects with words and images, but lack logical reasoning. These children love to play “pretend” and imagine. They are also very egocentric. For example, a child standing in front of a television may not understand why the person directly behind them cannot see the television because the child can see it perfectly well.

The third stage is the Concrete operational stage, ranging typically from 7 to 11 years of age. Here, children are able to think logically about concrete events, grasp concrete analogies, and perform arithmetical operations. Conservation is developed during this stage. Prior to this stage, children are unable to comprehend that a flat container and a tall container may hold the same amount of liquid because the tall container appears to have more. In this stage, however, children are able to better grasp concepts of size. Children are also able to perform mathematical functions and are capable of abstract logic.

The fourth stage is the formal operational stage. This stage begins around age 11 and continues into adulthood. In this stage, children are able to perform abstract reasoning. During this stage, moral and abstract reasoning develop and mature. Individuals in this stage are generally able to think hypothetically and rationally.