The psychologist Jean Piaget (1896-1980) of Switzerland is one the most seminal thinkers in the theory of childhood development. Piaget has postulated an Epigenetic Theory of Personality. Epi refers to emergence. The genetic refers to the core of natural material and socialization that comes to form the child. "So, in sum, genetic epistemology deals with both the formation and the meaning of knowledge. We can formulate our problem in the following terms: by what means does the human mind go from a state of less sufficient knowledge to a state of higher knowledge?" (Piaget, 1968).  Piaget's Stage Theory of Development was one of modern psychologies first attempts to comprehend how children progress through cognitive development. His original model describes four universal stages for children. They are:

·        The Sensormotor Period (birth to 2 years)

·        Preoperational Thought  (2 to 6/7 years)

·        Concrete Operations (6/7 years to 11years)

·        Formal Operations (11/12 to adult)

Piaget believed that performance of children was homogenous regardless of culture. It is a widely held position that not all children reach the formal operational period. This may be due to the socialization or externalities operating on a child under different environmental and cultural conditions (Berk, L.E. 2000). There is continued discussion on the movement of children through the development stages.

One of the most studied criticisms of Piagets work was by Lev Vygotsky of the socio-cultural school. Uriel Bronfennbrenner pertains to this perspective. Such postulates that in the positive correct nurturant external forces shape development more than innate a-priori factors. Regardless of revision, Piaget's methodology and work on the child are held by some to be equal to what Freud's work is to psychology in general.

The Sensormotor Period

At birth to two years all the intellectual and physical capabilities are underdeveloped. However the infant has sensory capabilities available. The infant learns by the exercise and utilization of reflexes in nexus with seeing, touching, sucking, feeling, and using their senses to learn things about themselves and the environment. Simple movements in response to stimuli later develop into more sophisticated coordinated acts of behavior(s). The infant through this limited expansion into its environment builds a set of concepts about reality and how it works. Object permanence or the knowledge that objects still exist after disappearing from sight has not been obtained by all children.

After a child has mastered the concept of object permanence, the emergence of directed groping begins to take place. The child begins to perform motor experiments in order to analyze the effects. A child will vary one's movements to observe differentiation in results. The child learns to use new means to achieve an end. The child discovers objects can be pulled towards oneself with the aid of a stick or string, or tilt objects to obtain such through the bars of a playpen.

Through trial and error experimentation by handling objects, the concept that the external world is not part of the self or an extension manifests. Piaget calls this the sensorimotor stage because the early manifestations of intelligence appear from sensory perceptions and motor activities (Anderson, M. 2003).