Adolescence refers to the period of development between the age at which a person becomes capable of sexual reproduction and adulthood. For most of human history, this time span has been only a few months, and this is still true in some cultures, where a sexually mature boy or girl is expected to marry and assume adult tasks. In modern Western societies, however, teenagers are not considered emotionally mature enough to assume the full rights, responsibilities, and roles of adulthood. In this section we'll examine the ups and downs of adolescence, starting with changes in the body and then turning to changes in the mind.

In middle childhood (ages 6 to 12), children go through a period called adrenarche (a-DREN-ar-kee), when the adrenal glands begin pumping out hormones that affect brain development, most notably an androgen called DHEA (Campbell, 2011). These hormones divert glucose in the brain to foster the maturation of brain regions vital to interpreting social and emotional cues. Indeed, children's brains during these years are at their most flexible and responsive to learning. Children become able to control their impulses, reason better, focus and plan for the future, and understand mortality and death. As children typically approach the end of middle childhood they enter puberty, the age at which a person becomes capable of sexual reproduction.

Until puberty, boys and girls produce roughly the same levels of androgens (masculinizing hormones) and estrogens (feminizing hormones). But from puberty on, boys have a higher level of androgens than girls do, and girls have a higher level of estrogens than boys do. In boys, the reproductive glands are the testes (testicles), which produce sperm; in girls, the reproductive glands are the ovaries, which release eggs. During puberty, these organs mature and the individual becomes capable of reproduction. In girls, signs of sexual maturity are the development of breasts and menarche, the onset of menstruation. In boys, the signs are the onset of nocturnal emissions and the growth of the testes, scrotum, and penis. Hormones are also responsible for the emergence of secondary sex characteristics, such as a deepened voice and facial and chest hair in boys and pubic hair in both sexes.

The onset of puberty depends on both biological and environmental factors. Menarche depends on a female's having a critical level of body fat, which is necessary to sustain a pregnancy and which triggers the hormonal changes associated with puberty. An increase in body fat among children in developed countries may help explain why the average age of puberty declined in Europe and North America until the mid-20th century. The average age of menarche now occurs at about 12 years and 6 months in white girls and a few months earlier in black girls (Anderson, Dallal, & Must, 2003). However, other signs of puberty in girls, such as pubic hair and breast buds, have been appearing at younger and younger ages; boys, too, are entering puberty 6 months to 2 years sooner than previously estimated.

The onset and length of puberty vary considerably. Some girls go through menarche at 9 or 10, or even earlier, and some boys are still growing in height after age 19. Early-maturing boys generally have a more positive view of their bodies than late-maturing boys do, and their relatively greater size and strength give them a boost in sports and the prestige that being a good athlete brings young men. But they are also more likely to smoke, drink alcohol, use other drugs, and break the law than later-maturing boys (Cota-Robles, Neiss, & Rowe, 2002; Rudolph et al., 2014). Some early-maturing girls have the prestige of being socially popular, but they are also more likely to fight with their parents, drop out of school, have a negative body image, abuse drugs, have poorer relationships, and be angry or depressed (Skoog, Özdemir, & Stattin, 2015; Westling, Andrews, & Peterson, 2012). Early menarche itself does not cause these problems; rather, it tends to accentuate existing behavioral problems and family conflicts. Girls who go through puberty relatively late, in contrast, have a more difficult time at first, but by the end of adolescence, many are happier with their appearance and are more popular than their early-maturing classmates (Beltz et al., 2014; Caspi & Moffitt, 1991; Stattin & Magnusson, 1990).

The media love sensational stories about teenagers who are angry or violent, live in emotional turmoil, feel lonely, have low self-esteem, and are running wild sexually. Parents and prosecutors have become so alarmed about “sexting,” the practice of emailing nude pictures to friends, that adolescents in the United States and Canada have been convicted on charges of creating and distributing child pornography. Yet in reality, overall feelings of self-esteem do not suddenly plummet after the age of 13 for boys or girls (Gentile et al., 2009), and the rate of violent crimes committed by adolescents has been dropping steadily since 1993. As for sex, according to the National Youth Risk Behavior Survey, today's high school students are actually more conservative than their parents were at their age; fewer are having sex, and among those who are, the number of partners has declined (Rosin, 2012).

Similarly, studies of representative samples of adolescents find that only a minority are seriously troubled, angry, or unhappy. Nevertheless, three kinds of problems are more common during adolescence than during childhood or adulthood: conflict with parents, mood swings and depression, and higher rates of reckless, rule-breaking, and risky behavior (Steinberg, 2007). Rule breaking often occurs because teenagers are developing their own standards and values by trying on the styles, actions, and attitudes of their peers, in contrast to those of their parents.

Peers become especially influential in adolescence because they represent the values and style of the generation that teenagers identify with, the generation that they will share experiences with as adults (Bukowski, 2001; Harris, 2009; Smith, Chein, & Steinberg, 2014). Many people report that feeling rejected by their peers when they were teenagers was more devastating than punitive treatment by parents. According to a government-sponsored review of whether and how online technologies affect child safety, the most frequent dangers that teenagers face on the Internet are not pornography or even predatory adults, and definitely not sexting. “Bullying and harassment, most often by peers, are the most frequent threats that minors face, both online and offline,” the report found (Berkman Center for Internet & Society, 2008, 2012).

Adolescents who are lonely, depressed, anxious, or angry tend to express these concerns in ways characteristic of their sex. Boys are more likely than girls to externalize their problems in acts of aggression and other antisocial behavior. Girls are more likely to internalize their feelings and problems by becoming withdrawn, blaming themselves for whatever goes wrong, or developing eating disorders (Wicks-Nelson & Israel, 2003). In general, girls are more dissatisfied than boys with their bodies and general appearance; boys are more dissatisfied than girls with their social behavior at school and with friends (Gentile et al., 2009).

Keep in mind that the “psychology of adolescence” depends profoundly on the larger culture in which teenagers live. During the 1960s and early 1970s, a period of great social upheaval during which many teenagers rebelled against their parents' lives and values, some observers wrote as if teenage rebellion were a universal, biologically driven phase; today, most teenagers remain close to their parents and see no reason to rebel against them. In this light, consider the role of culture's influence on a particular personality trait, narcissism. Narcissism is not the same thing as self-esteem; it is a combination of excessive self-regard and a lack of empathy or interest in others (Twenge, 2013). And it is not the kind of understandable self-focus that is common among adolescents and young adults who are worried about their future relationships and work lives (Roberts, Edmonds, & Grijalva, 2010).

Jean Twenge and her colleagues (2008) have amassed considerable evidence that narcissism has been rising among today's cohort of college students and younger teenagers, to such a degree that they refer to this cohort as “Generation Me.” American college students' scores on the Narcissistic Personality Inventory, which measures a grandiose sense of importance, entitlement, and cynicism (narcissists agree that “I wish somebody would someday write my biography” and “I find it easy to manipulate people”), have steadily increased between the years 1982 and 2008 (Twenge et al., 2008; Twenge & Foster, 2010). Why? One answer, they suggest, is that we live in a time in which American culture has become more self-focused and less other-directed. Consider, for example, the relatively recent “selfie” culture, and the popularity of the phrase, “Pics or it didn't happen!” There's a generation of people focused on documenting every aspect of their lives, with themselves as the center of attention. Do you think these research findings sound reflective of today's youth culture? Why or why not?

Predicting Adolescent Behavior