http://psychology.about.com/od/behavioralpsychology/l/bl-piaget-stages.htm

Jean Piaget divided the cognitive stages into four parts.  He did this because he understood that children learn and understand differently as they get older.

Jean Piaget the psychologist who developed the cognitive theory due to the years he spent observing children will forever be remembered as one of the most influential psychologists in history.

http://www.simplypsychology.org/piaget.html