Swiss biologist, Jean Piaget is renowned for constructing a highly influential model of child development and learning. His theory is based on the idea that the developing child builds cognitive structures for understanding and responding to physical experiences within his environment. Piaget's theory identifies four developmental stages: sensorimotor stage, preoperational stage, concrete operations, and formal operations.
During the first stage, sensorimotor (birth-2 years old), a child's cognitive system is limited to motor reflexes at birth, but the child builds on these reflexes to develop more sophisticated procedures. They learn to generalize their activities to a wider range of situations and coordinate them into increasingly lengthy chains of behavior. Through physical interaction with his environment, the child builds a set of concepts about reality and how it works. This is the stage where a child does not know that physical objects remain in existence even when out of sight, known as object permanence.
A child's intelligence is demonstrated through motor activity without the use of symbols. This allows the child to begin developing new intellectual abilities. Towards the end of this stage, some symbolic abilities are developed.
The second of Piaget's stages is the preoperational stage (2-7 years old). In this period, intelligence is demonstrated through the use of symbols, language use matures, and memory and imagination are developed, but thinking is done in a nonlogical, nonreversible manner. The child in this stage is not yet able to conceptualize abstractly and needs concrete physical situations. From 2 to 7 years old, children demonstrate an increased ability to use symbols to represent real objects in their environment. Children in this stage have difficulties seeing another's point of view, known as egocentrism. Piaget used the famous mountain task to study the egocentrism of young children. When shown a model of 3 mountains,