Adolescence is both biological and social in nature. The beginning of adolescence is marked by biological changes in girls and boys. As a matter of fact, just before puberty there occurs what is known as pre-adolescent growth spurt. It takes place in girls mostly during the age of nine to twelve years, and in boys between eleven and fourteen years of age. During this period, and following shortly thereafter, the secondary sexual characteristics emerge. In girls there is typically rounding out of

the hips, breast development, appearance of pubic hair, and menstruation. In boys, some of the secondary sexual characteristics that mark the beginning of adolescence are appearance of pubic hair, facial hair, and change of voice. These changes are biologically induced. 

Adolescence for both girls and boys is marked largely by social changes. Such factors as when an adolescent leaves home, gets a job and can vote determine when his or her transition from childhood to adulthood is accomplished. The length of this period is thus primarily a social phenomenon. 

The problems adolescents face during the long period of growing up have both biological and social roots. Physical changes and deviation can create many problems. Society also creates problems for adolescents. Adolescents in western societies behave differently than adolescents in eastern societies owing to varying social norms, expectations and family structure.