Between the ages of 11 and 18, young people cross the great divide between childhood and adulthood. This crossing encompasses all three domains of development—biosocial, cognitive, and psychosocial. Chapter 9 focuses on the dramatic changes that occur in the biosocial domain, beginning with puberty and the growth spurt. The biosocial metamorphosis of the adolescent is discussed in detail, with emphasis on factors that affect the age of puberty, sexual maturation, and changes in body rhythms. Although adolescence is, in many ways, a healthy time of life, the text also addresses two health hazards that affect many adolescents: sex too early and sexually transmitted illnesses.
Chapter 9 also describes the cognitive advances and limitations of adolescence. With the attainment of formal operational thought, the developing person becomes able to think in an adult way—that is, to be logical, to think in terms of possibilities, and to reason scientifically and abstractly. Neurological development is the basis of these new developments. Although brain areas dedicated to emotional arousal mature before those dedicated to emotional regulation, ongoing myelination enables faster and deeper thinking.
Even those who reach the stage of formal operational thought spend much of their time thinking at less-advanced levels. The discussion of adolescent egocentrism supports this generalization in showing that adolescents have difficulty thinking rationally about themselves and their immediate experiences. Adolescent egocentrism makes them see themselves as psychologically unique and more socially significant than they really are.
The final section of chapter 9 explores teaching and learning in middle school and high school. As adolescents enter secondary school, their grades often suffer and their level of participation decreases. The rigid behavioral demands and intensified competition of most secondary schools do not, unfortunately, provide a