Adolescence is a period in life when people grow more rapidly than at any other time in their lives except infancy.

For girls, this rapid growth spurt usually begins at age 10, with the peak occurring at about age 12. The growth spurt for boys begins about a year later, at around age 11 '/z and peaks at around age 14.
Changes in physical appearance are the most striking aspects of physical development, but invisible changes also take place. Three kinds of physical changes occur during young adolescence: (1) the adolescent growth spurt; (2) the development of primary sex characteristics; and (3) the appearance of secondary sex characteristics.

The adolescent growth spurt includes the growth to nearly the full adult height in both boys and girls. Their bodies may ache from all the internal activity. Limbs can grow quickly and unevenly, which accounts for the clumsiness that often emerges in adolescence. For example, an arm may grow half an inch in two weeks. Co-ordination can be a problem at this point, as the brain cannot keep up with the body to negotiate anything close to graceful movement. Further, the adolescent metabolism rate is very high, resulting in periods of boundless energy followed by total lethargy. Adolescents are not able to tell us what is happening in their bodies, but they act it out in their behavior. They can be clumsy, tired, energetic or hungry as a result of their growing bodies. It is unfair to interpret their behavior as careless, lazy or rambunctious without recognizing the biology that is at work.

From Child to Adult Bodies

Although it is an entirely common experience for people to grow from child to adult bodies, the individual growth patterns are highly personal. Early physical developers do not always demonstrate early intellectual and social growth.  Developmental diversity is the hallmark of adolescence. That information needs to affect our approach to young adolescents. Further, they need to know that their individual biological clocks are ticking "normally."

It is during adolescence that the reproductive systems mature. These changes are called primary sex characteristics. For girls, the marker event is the beginning of the menstrual cycle. It can begin as early as 10'/z or as late as 15 years. The average age for a young woman to begin menstruating is 12 'h. Her breasts grow, a little or a lot, depending on the body shape she has inherited. The uterus and vagina grow and eggs in ovaries mature, and she is able to become pregnant. For boys, the marker events are genital growth and the first ejaculation. His penis and testicles grow larger and he is able to produce semen and sperm. Both young men and women begin to have strong sexual/romantic feelings. There is a wide variation in the ages at which these events begin to occur.

Secondary sex characteristics are the more obvious and perhaps the most concerning to adolescents. The hair on their legs and underarms grows thicker, darker. Body shapes begin to develop. Hips get bigger, body weight shifts in young women. Muscular strength increases and shoulders broaden in a young man. His voice lowers and whiskers start to grow on his face. Both young women and men experience their skin becoming oilier and their sweat glands begin to work. During the events of puberty bodies look, smell, act and feel differently.

Growth in each developmental area (physical, cognitive, social and emotional) occurs in a characteristic sequence for most young adolescents. However, growth in the four areas does not occur exactly at the same time. Young adolescents may vary enormously in physical, mental, emotional maturity. For example, early physical developers do not always demonstrate early intellectual and social growth.

Furthermore, individual young adolescents change at different rates, according to highly individual internal "clocks." For example, a 13-year-old who looks like a young woman or man is as "normal" as peers who are only beginning to mature physically, and a 12-year-old concrete thinker is as normal as a 14-year-old who uses abstract reasoning rather expertly.

Adults must be careful not to base their treatment of young adolescents solely on one aspect of their development. For example, the physically mature into roles of leadership based on an assumption of parallel emotional maturity.

The normal variation in young adolescent physical development means that there may be a six- to eight-year span in physical development between a slowly developing boy and a rapidly developing girl of the same chronological age. Physical ability is entirely related to individual body clocks, not ability or effort. Given these circumstances, competitive physical activity with this age group is simply unjust.

Body Awareness

It is important to make a distinction between a body-based experience and a sexually-based experience. Especially for younger adolescents, the body changes (i.e., the growth spurt) is a body-based experience and is not sexually aware, or informed. The young adolescent is aware of body first and sexuality secondarily. The minor watching and the preening and the self-consciousness are based on the experience of a body that is changing. The awareness of the sexual implications and potential does not lead and direct that process but grows out of it. Adults assume the opposite and often react as if body sensitivity is actually some immense sexual discovery. In the myth of adolescents as "walking hormones," adults forget how innocently the process of change begins with growth and size changes that then gradually include sexual development.

For early and fast developers, this is compressed together in terms of experience. The physical changes and the sexual development are close together. In late developers, the experience can be quite different with a very long physical development occurring before and after sexual maturation, making body experience and awareness quite different. This complicates the body image question for adolescents at either end of the continuum. Those in mid-continuum get body awareness first and sexuality develops in the context of an already changing image and self-awareness.

There is not much tidiness as the variety of knowledge that adolescents have is so varied. Their experience is not formed by their knowledge, but by their physical experience of the body in change, day by day. Sexual development is only part of that process and may not be the focus for adolescents all the time. It is not helpful for adolescents to have to cope with adults assuming they are preoccupied with sex.

Adolescents must also contend with images in the media on a daily basis of the perfect body. Their appearance is judged by their friends, by the other sex and by their parents. Boys work out with weights, girls begin to shave their legs and begin the struggle for the perfect look that may continue for the rest of their lives.