During adolescence, children experience a rapid increase in height and weight. This growth spurt is highly variable, generally lasting 24-36 months. Females typically experience this growth spurt one-and-one-half to two years earlier than males and on average grow 23-28cm. Male average growth is 26-28cm. The growth spurt ends with epiphyseal closure, which is under the influence of the sex steroids. Males experience a 2-year delay in bone closure as compared to females, and this accounts in part for their greater growth in height.

In addition to increases in height, teens experience increases in weight. About 50% of adult ideal body weight is gained during puberty. Adolescent male weight gain primarily reflects an increase in lean body mass. In contrast, adolescent females experience an increase in percentage of body fat and a decrease in percentage of lean body mass.

Body structures also have dissimilar growth rates. The first structures to reach their adult size are hands, feet and head. Leg length reaches its peak before body breadth. This sequence of growth can give teenagers a long-legged appearance and lead to clumsiness and tripping (Tanner, 1972).

Cognitive Development

Adolescence is also marked by major changes in cognitive thinking. During adolescence, teens move from concrete thinking to what psychologist Jean Piaget (1969) calls the period of formal operations. When functioning at the concrete operational level, teens cannot transcend the immediate and are unable to deal with remote, future or hypothetical problems. In contrast, formal operations functioning allows the individual to "think about their own thinking," transfer information from one situation to another, deal efficiently with the complex problems involved in reasoning, plan realistically for the future and conceptualize abstract ideas. Not all teens or adults attain full formal operational thought. In fact, more than one-third of college students and middle-aged adults do not use formal operations when faced with the need to solve an unfamiliar problem (Keating & Clark, 1980).

As the young adolescent moves toward abstract reasoning, a new type of introspection occurs. Daydreaming, increased self-interest and fantasy are common. This is frequently manifested in young teens by spending hours examining every aspect of their appearance in front of a mirror. Adolescents assume that others are as interested in their thoughts and actions as they are. They view the world as a stage on which they are the principal actors and the entire world their audience. They see themselves as unique and destined for unusual fame and fortune. Psychologist David Elkind (1968) refers to this form of egocentrism as the "personal fable." By age 15 or 16 this type of egocentrism decreases.

Young adolescents, at the beginning of this cognitive shift, have unrealistic career plans with visions of an idealized future, i.e., as a rock star or pro basketball player. By middle adolescence, they begin to have more realistic career goals and begin to realize their limitations. For teens in disadvantaged situations, this may lead to the beginning of feelings of hopelessness. Ideally, the late adolescent will have realistic career goals, a sense of perspective, be able to problem solve, consider all aspects of a situation, and delay gratification.