Adolescence is a notoriously confusing time for young people and their parents, but it's also a very exciting time of life, as your child slowly becomes a full grown adult, capable of making his or her own decisions and managing life more independently. The actual period of adolescence is defined as the years between the onset of physical and psychological adolescent development, beginning at around age 11 (although in the West many kids start earlier) and ending at around age 18 to 20. A child begins this process as, well, a child, and ends it as a physically (if not always emotionally!) mature adult.
Many of the physical and emotional changes a young person goes through during these years are driven by increased production of sex hormones (namely testosterone in boys and estrogen in girls). These hormones can also give rise to mood swings and thereby cause possible conflict within a family. For parents who want to learn more about adolescent development, there are a plenty of adolescent development articles online. If you are concerned about some aspect of your child or teenager's development, consult your family doctor.
Adolescent Physical Development
During adolescence, boys go through a growth spurt and become taller, sometimes very quickly indeed. Their voices become gradually deeper, which can cause a lot of embarrassment if they initially find it hard to control the pitch of their voice when they are talking. Their genitals become larger, and pubic hair grows, as well as hair on the legs, arms, underarms, chest, face, etc. Boys will have to begin shaving. Personal hygiene becomes more important as body odor is possible after sweating - at this stage boys have to begin using underarm deodorant.
Girls also experience a growth spurt during adolescence and may gain height quite quickly. It's also normal for girls to gain weight within a healthy limit and to develop more womanly features (such as curvy hips). The breasts begin to develop and pubic hair grows, as well as hair under the arms and on the legs - girls may feel self-conscious about this and want to start shaving these areas. Menstruation usually begins a couple of years after the breasts first start to grow, but not always. Girls have been known to begin having periods as young as 9 years old, although this is very rare.
Adolescent Social Development
Social development during adolescence is very closely tied in with adolescent emotional development, and can be the most exasperating part of the process for many parents. At this stage of life, teenagers are working out who they are, and they often do this by comparing themselves to their peers or attaching themselves to a certain social group or dress code. Parents find it difficult to understand their teenagers' choice of clothing and may find themselves being accused of unjustifiable cruelty for refusing to buy "that shirt." It's all part of the experience of raising children, and generally speaking, it comes to an end within a few years providing that adolescents are set boundaries. There's a theory that if you want your teenager to rebel "safely" you should set your boundaries high - much better for her to experiment with dark eye make-up, which she knows you don't like, than to stay out all night because you said she could come back at 2 am, and she wants to test you, right? Of course, this doesn't work for every family, and parents have to determine the right way to interact with their own teenage children. If you're concerned about your child, or if he or she is showing signs of depression (it can happen during this development period) speak to your health care provider.
Adolescent Brain Development
One concerning aspect of adolescent cognitive development during the teenage years is the conflict between the brain's heightened ability to appreciate rewards and pleasure, versus the only gradual development of impulse controlling abilities. Changes that take place in the frontal lobe of an adolescent's brain mean that "fun" things feel even better than they did when the teenager was younger, however, now the types of things that she finds fun aren't harmless cartoons or games. Some adolescents find pleasure in risk taking behaviors in particular. This can manifest itself in increased enjoyment of scary fun park rides (roller coasters) or in something more dangerous and possibly illegal (racing cars). Because the ability to control impulses may not be fully developed until a person enters her 20s, adolescents and teenagers still need a lot of guidance from their parents to help them stay safe.