Swiss Psychologist Jean Piaget (1896-1980) proposed the idea of the four stages of childhood cognitive development. These are age-related stages and refer to certain accomplishments that should be achieved, by the child, at the end of each stage. The first stage of cognitive development is the Sensorimotor stage, which lasts from birth to around two years of age. During this stage, children learn to coordinate their senses (hearing, sight, touch etc.) with their motor abilities. …showed first 75 words of 316 total…

…showed last 75 words of 316 total…is shown the plasticine and agrees that the balls are the same size. One of the balls is then squashed down. A pre-concrete operational child will probably decide that the 'squashed' ball is bigger, while a child at the Concrete operational stage should acknowledge that they are still the same weight or mass. This illustrates the ability of the child to understand how the object has changed, not only see the beginning and end result.