Reasons behind why children think in different ways have been established in various theories. Jean Piaget advanced a greatly influential theory that reflected his prior studies in the fields of biology and genetic epistemology. It is a theory that has been contended by many others, including that of the information-processing approach to cognitive development. It will be shown where these theories compare and where they contrast, in conclusion explaining why Mary's children think differently.
Introduction
The cognitive abilities of children have long been an issue for developmental psychologists. The development of a child's mental processes, such as thinking, remembering, learning and using language, has been interpreted by many psychologists and explained in a number of theories. Of these theories Jean Piaget's cognitive developmental theory has been a major influential model since its origination in the 1920s (Beard, 1969 ). Piaget's theory has a biological perspective to cognitive development and focuses on broad, qualitative stages. Another acknowledged theory is the information- processing theory which, approaches cognitive development from a computer accentuated perspective, and focuses on the more narrow, continuous, quantitative changes (Westen, 1996).

Though these theories approach cognitive development from different angles, their advancements into how a child constructs thought and thinks are not totally at odds with one another as they similarly compare in some aspects.

This essay will discuss how these two theories compare and contrast, and in conclusion elucidate why Mary's seven-year-old son sometimes thinks very differently to his three-year-old brother.

Body of Evidence

The Piagetian theory of cognitive development emphasises the relationship between biological and physiological functioning (Hughes and Noppe, 1990) and the individual and the environment. Piaget developed his theory following observations conducted with children of varying ages that deduced that children of different age groups gave consistently different answers from children in other age groups (Beard, 1969). The reasoning behind these answers seemed to have more significance then the actual answers as Piaget asserted that these responses reflected the variance in children's thinking, thus suggesting cognitive development occurred in a stage-like process (Matlin, 1983).

Preceding the commencement of the four identified stages, Piaget stated that there is a process that can be described as 'coming to know' (Tuddenham, 1972) , this acquisition of cognitive abilities are then gradually accumulated throughout the stages.

The process of 'coming to know' commences with the infant's innate reflexes and their innate tendency to exercise them in certain situations (Beard, 1969). These reflexes are simplistic schemes, which Piaget referred to as an organised, repeatedly exercised pattern of thought or behaviour (Westen 1996). Schemas being the earliest forms of mental activity a young infant develops (Matlin 1983), gradually increase in quantity and advance in complexity with maturation, thus enabling thinking and behaviours to a more complex degree (Wilkes, 1997 ). In order for schemas to develop, two processes are constantly utilised to maintain what Piaget is asserted is the driving force behind cognitive development, equilibrium (Westen, 1996). Assimilation and accommodation are used simultaneously and alternately throughout development allowing adaptation and organisation and thus, equilibration (Wilkes, 1997).

Once these cognitive abilities are acquired, Piaget suggested that they gradually develop through four qualitatively different stages that proceed successively. Although they occur in an exact sequence, they are not strictly determined by age Each stage equips the child with distinct logic capabilities that are requisites for the next stage of thinking (Deiner, 1996).

The sensorimotor stage extends from birth to age two, a period that sees the beginning of physical development. While this development enables increasing physical interaction with the environment, ...