Jean Piaget studied cognitive development among children of different age groups in different developmental stages. These stages are (sequentially):Sensorimotor stage: (birth to 2 years)Pre-operational stage: (2 to 6 years)Concrete operational stage: (6 to 11 years)Formal operational stage: (11+ to adolescence and adulthood)Additional Information Jean Piaget is a Psychologist from Switzerland who proposed that development is based on Physical environment and Biological abilities.He ignores Social aspects in development.StagesChanges in childSensorimotor stageSenses are teachersReflex actions.Intimate behavior. Pre-operational stageLanguage developmentIrreversibilityEgocentrismAnimismConcrete operational stageLogic beginsReversibilityClassificationConservationFormal operational stageGeneral to specific.Divergent/Convergent.Creative thinking.