Developmental stage theories
There are a number of different views about the way in which psychological and physical development proceed throughout the life span. In addition to individual differences in development, developmental psychologists generally agree that development occurs in an orderly way and in different areas simultaneously.
Continuous versus discontinuous development
One of the major controversies in developmental psychology centres whether development is continuous or discontinuous. Those psychologists who support the continuous view of development suggest that development involves gradual and ongoing changes throughout the life span, with behaviour in the earlier stages of development providing the basis of skills and abilities required for the next stages.
Not all psychologists, however, agree that development is a continuous process. Some view development as a discontinuous process. They believe development involves distinct and separate stages with different kinds of behaviour occurring in each stage. This suggests that the development of certain abilities in each stage, such as specific emotions or ways of thinking, have a definite starting and ending point. However, there is no exact time at which an ability suddenly appears or disappears. Although some types of thinking, feeling or behaving may seem to appear suddenly, it is more than likely that this has been developing gradually for some time.
Stage theories of development rest on the assumption that development is a discontinuous process involving distinct stages which are characterized by qualitative differences in behaviour. They also assume that the structure of the stages is not variable according to each individual, however the time of each stage may vary individually. Stage theories can be contrasted with continuous theories, which posit that development is an incremental process.
Examples of stage theories
There are many stage (discontinuous) theories in developmental psychology including:
- Sigmund Freud's Psychosexual stages described the progression of an individual's unconscious desires. (1900s-1920s)
- Rudolf Steiner's seven-year phases, similar to Piaget's stage theory but extending into adulthood. (1907) 
- Jean Piaget's theory of cognitive development described how children represent and reason about the world (1920s-1930s).
- Lawrence Kohlberg's stages of moral development described how individuals developed moral reasoning. (1958)
- Erik Erikson's stages of psychosocial development expanded on Freud's psychosexual stages, he defined eight stages that describe how individuals relate to their social world. (1959) 
- Margaret Mahler's separation-individuation theory of child development contained three phases regarding the child's object relations.
While some of these theories focus primarily on the healthy development of children, others propose stages that are characterized by a maturity rarely reached before old age.
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- White, F., Hayes, B., & Livesey, D. (2005). Developmental Psychology: From Infancy to Adulthood. NSW:Pearson Education Australia
- Lievegoed, Bernard (1997). Phases: the spiritual rhythms of adult life. Forest Row, GB: Rudolf Steiner Press. ISBN 1-85584-056-1.
- Kohlberg, L. (1987). The Measurement of Moral Judgement. Cambridge: Cambridge University Press. ISBN 0-521-32565-X.
- Maslow, A. H. (1987). Motivation and personality (3rd ed.). New York: Harper & Row. ISBN 0-06-041987-3.