However, this is a very simplistic distinction - most people really fall on a scale from one extreme to the other, with few of us entirely introverted or extraverted. Sometimes researchers use the term 'ambivert' to mean someone who is more or less equally balanced between the two.
The following image illustrates this idea of a scale between two extremes:
|Introversion v's extraversion. Source: here.|
According to researcher Hans Eysenck (1967), some people have a less sensitive nervous system than others do, and therefore need more environmental input for the same end result. They therefore need more social interaction in order to feel stimulated causing them to be extraverted, while those with more sensitive nervous systems feel overwhelmed with too much input, and therefore avoid it i.e. they are introverted. This biological theory is supported by evidence suggesting that personality appears early in life, and that personality traits remain steady over the lifespan (McCrae & Costa, 1997).
The work of McCrae and Costa (1997) suggests that personality factors including extraversion are universal, and therefore relatively little influenced by culture. The society that we live in does make a difference to whether traits are encouraged or even accepted, however; in her 2013 book 'Quiet', Susan Cain argues that society increasingly values the extravert, with introverts being misunderstood and undervalued.
From a teaching point of view, it is undoubtedly true that the typical classroom today - with discussions, debates, and a social-constructivist approach to learning in general - is more geared to the extravert than to the introvert.
Eysenck, H. J. (1967). The Biological Basis of Personality. Springfield, IL: Thomas Publishing.
McCrae, R.R. and Costa, P.T. Jr (1997). Personality trait structure as a human universal. American Psychologist, 52(5), 509-516.