Adolescent Psychology addresses the specific issues of adolescents.
Adolescence, the transitional stage of development between childhood and adulthood, represents the period of time during which a person experiences a variety of biological changes and encounters a number of emotional issues. The ages which are considered to be part of adolescence vary by culture, and ranges from preteens to nineteen years. According to the World Health Organization (WHO), adolescence covers the period of life between 10 and 20 years of age. Adolescence is often divided by psychologists into three distinct phases: early, mid and late adolescence.
Adolescence can be a specifically turbulent as well as a dynamic period of one's life. It has been identified as a period in which young people develop abstract thinking abilities, become more aware of their sexuality, develop a clearer sense of psychological identity, and increase their independence from parents.  G. Stanley Hall denoted this period as one of "Storm and Stress" and, according to him, conflict at this developmental stage is normal and not unusual. Margaret Mead, on the other hand, attributed the behavior of adolescents to their culture and upbringing.
Several developmental stage models have placed adolescence in a period of human development. Sigmund Freud saw it as the "genital phase" of psychosexual development, where the child recaptures the sexual awareness of infancy. Jean Piaget focused on cognitive development, seeing adolescence as the "formal operative stage" where the young person develops the ability to think abstractly and draw conclusions from the information available. Erik Erikson’s theory of psychosocial development identified the identity crisis as central to the notion of adolescence.
Adolescent psychology addresses the issues associated with adolescence, such as whether or not the aforementioned "storm and stress" is a normal part of this period. The American Psychological Association has a separate division dedicated to adolescence, and the psychologists specializing in this topic attempt to answer questions dealing with the age group. One issue in adolescent psychology discusses whether adolescence is in fact a discrete developmental period, a point along a continuum of human development, or a social construction.
Social behavior patterns
The social behavior of mammals changes as they enter adolescence. In humans, adolescents typically increase the amount of time spent with their peers. Nearly eight hours are usually spent communicating with others, but only eight percent of this time is spent talking to adults. Adolescents report that they are far happier spending time with similarly aged peers as compared to adults. Consequently, conflict between adolescents and their parents increase at this time. These interactions are not always positive; peer pressure is very prevalent during adolescence, leading to increases in cheating and misdemeanor crime. Young adolescents are particularly susceptible to conforming to the behavior of their peers.
Non-human mammals also exhibit changes in social attitude during adolescence. Adolescent rodents have also been observed spending more of their time with rodents of similar age. Conflicts between adolescents and parents have been noted in other primates, and overall increases in aggressiveness have been observed during this time period. Despite this, social bonding between adolescents and adults tends to improve due to reconciliatory behavior. Allomaternal behavior increases among females in several species, including humans, nonhuman primates, and rodents. However, males tend to exhibit less interest in infants during adolescence.
Early adolescence is a stage at which the peer group becomes increasingly important, with conformity to peers peaking at 11-13 years (Costanzo and Shaw 1966). 90% of adolescents identify themselves with a peer group (Palmonari, 1989). According to Judith Rich Harris’s theory of group socialization, children and adolescents are shaped more by their peers than their parents (Harris 1997). Peers can encourage both pro-social behavior, which peaks at 11-12 years, or anti-social behavior, which peaks at 14-15 years (Bendt, 1979). Adolescents are less likely to feel depressed or anxious if the peer group provides emotional support (Buhrmester, 1992).
Searching for a unique identity is one of the problems that adolescents often face. At this age, role models such as sports players, rock stars and movie and television performers are very popular, and adolescents often express a desire to be like their chosen role model.
Adolescents may be prone to recklessness and risk-taking behaviors, which can lead to substance abuse, car accidents, unsafe sex and youth crime.  There is some evidence that this risk-taking is biologically driven, caused by the social and emotional part of the brain developing faster than the cognitive-control part of the brain. 
Although most adolescents are psychologically healthy, they can (like adults) exhibit signs of mental illness. Late adolescence and early adulthood are peak years for the onset of schizophrenia. Mood disorders such as clinical depression and bipolar disorder can initially show in adolescence.   Girls aged between 15 and 19 make up 40% of anorexia nervosa cases. 
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