An understanding of adolescence begins with recognition that different sets of changes occur along separate trajectories during the second decade of life—and that changes in each arena affect developments in others. It is also important to note the significant individual differences in the ways that children experience these changes. Some aspects of puberty, such as the onset of biological changes, begin at younger ages today than a century ago (at around age eight for girls and nine for boys): children grow in stature and begin to develop the physical characteristics of adults earlier; production of the hormones that control sexual development increases and leads to reproductive maturity at younger ages. In many traditional societies, the interval between attaining puberty and taking on adult roles (such as marriage and employment) was typically two to four years. More recently, this interval has stretched to an 8- to 15-year period, creating a prolonged period of dependency, and stretching out the acquisition of the skills and responsibilities of adulthood. Some of the workshop participants indicated that this lengthening of the transition period may be one of the most important sources of change in the adolescent period over the past 100 years. It has also stimulated the development of a new set of studies focused on the population of 18- to 25-year-olds, who are increasingly viewed as encountering a separate stage of development termed “emerging adulthood.”

Changes in mood and emotions occur during adolescence as well—as parents frequently observe, teenagers may rather suddenly display such changes as new emotional intensity, increased interest in romance, increases in risk-taking, and changes in sleep patterns. These affective developments may also be linked to the endocrine system, although the mechanisms through which this takes place are less well understood.

Cognitive maturation typically occurs less suddenly, Dahl noted, and is independent of sexual development. It correlates more with age and maturity, and new research has been emphasizing that fundamental changes in brain development occur much later than had been recognized—continuing long after puberty is over. Children’s capacities for logic, reasoning, and planning continue to grow throughout adolescence, as do their problem-solving skills and capacity to understand the long-term consequences of their behavior—these capacities are far from fully developed as puberty is reached.

The slower pace and more diffuse nature of cognitive development—and the fact that it occurs independently of other developmental changes—

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