Freud believed that the first years of an individual are crucial to its well balanced personality. Even if he said that the adult personality has a certain degree of flexibility, he also believed that by the time adulthood is reached, the basic structure and functioning of a human personality is set during the first five or six years of life
Skinner is considered the successor of Watson who said once that psychology was not a study of the mind but more a science of behavior.
Watson insisted that psychology must focus on “the study of observable conditions” and be objective.
Watson was extreme in his beliefs, by saying for example that he could turn any healthy child into a lawyer, an artist or a thief, just by providing the right environment
The Piaget theory is the study of cognitive development showing how children gradually learn the concepts of cause and effect, the knowledge of time and space, and how they acquire numbers. Gradually, they learn how to apply all those concepts, and also how to think logically and use their imaginations