Jean Piaget, a Swiss cognitive theorist who believed that children's learning depends on reinforcements, such as rewards from adults. According to his cognitive-developmental theory, children actively construct knowledge as they explore their world (Berk, 2008). Piaget separated cognitive development into 4 main stages which he called Sensorimotor, Pre-Operational, Concretely Operational and Formal Operational. According to Piaget, this sequence is invariant; all children will progress through the stages in the same order. Say no to plagiarism. Get a tailor-made essay on “Why violent video games should not be banned”? Get an original essay During the sensorimotor phase, from birth until around 18-24 months, infants are not yet capable of use symbols or images to represent objects in the external world (Essa, 2009). To think about an object, they must act on it with their senses and motor skills. The major advancement of this stage is object permanence, the understanding that objects continue to exist outside of sensory awareness. If a baby reaches for a toy and you cover it with a cloth, he will stop reaching for it and look at something else. If you secretly remove the toy and then lift the fabric, the baby will look at the empty place without surprise or disappointment. According to Piaget, the baby does not yet have object permanence; out of sight is out of mind. Around the age of one, children develop object permanence and can use mental representation and think about objects that are not physically present. From approximately 2 years to 7 years, the child is in the preoperative stage of development. They can now use mental representation to think. They start pretending. Children are now capable of symbolic representation – using a symbol to represent an object (Berk, 2008). Thanks to this, children learn a language, a system of symbols. Piaget emphasized that during this period, children's abilities are limited. A pervasive limitation in children's reasoning during the preoperative period is egocentrism, the inability to take another person's point of view. A child may assume that everyone has the same knowledge, experiences, and perspectives as him. Egocentric thinking predominates. The concrete operational phase lasts approximately between 7 and 11 years. Now children can engage in mental representation and think logically about the world around them (Essa, 2009). More specifically, children are able to manipulate their mental representations to think and solve problems. Thought becomes logical, overcoming the limitations of the preoperative phase of reasoning. Children are now able to understand conservation, that a change in the size or shape of a substance (like clay) does not change its mass. Operational thinking develops (reversible mental actions). Self-centered thinking diminishes. At the beginning of adolescence, individuals enter Piaget's period of formal operations. Cognitive development is now reaching its peak. Adolescents become able to use and manipulate their symbolic representations in abstract thought. They can create and think logically about hypothetical situations. Scientific and deductive reasoning becomes possible. The individual is cognitively mature. At the beginning of this period, we see a return to egocentric thinking. Only 35% of high school graduates in industrialized countries obtain formal operations; many people do not think formally about age..