Puberty is the natural process that a child's body undergoes during adolescence. During puberty, the human body matures into an adult body that is capable of human reproduction. A British physician named James Tanner developed a commonly used scale that contains several stages in puberty used to track the development of the human body. Known as the Tanner scale, stages II through V are the most critical in observing the growth of a body via puberty.
For boys, Tanner stage II is the beginning of the physical changes triggered by puberty and starts between the ages of 9 and 14. Puberty starts when the brain's pituitary gland releases hormones through the rest of the body. These hormones, called gondadotropins, cause the testes to grow, thus releasing another hormone called testosterone to be secreted through the body. Testosterone causes most of the puberty-related changes in a male body.
Puberty begins in girls exactly like it does for boys, through the release of gonadotropins to the rest of the body. The ovaries in a girl's body then begin to enlarge and release a hormone called estrogen. Estrogen serves as the catalyst to most female changes throughout puberty. A girl's breasts, genitals and uterus will begin growing and developing in response to estrogen. Typically, girls also grow in height and weight during this stage. Girls between 8 to 13 years old will experience this stage in puberty.
In Tanner stage III, a boy's scrotum and testes will continue to grow, and the penis will begin to lenghten. Pubic hair becomes thicker and more prevalent, and his voice begins to deepen. Boys also become taller, and their muscles begin developing. Boys reach this stage between 10 and 14 years old.
Girls experience breast growth during this stage. The uterus, vagina and genitals also develop. Pubic hair becomes more noticeable and spreads out farther. Girls continue to become taller and develop a definitive shape. Girls tend to experience this stage of puberty between the ages of 9 and 14.
During Tanner stage IV, a boy's scrotum, testes and penis continue to grow in length and width, via testosterone. Sperm begins to develop, and boys begin to have their first sustained erections and "wet dreams." Boys also begin to grow facial and underarm hair, rapidly grow taller and develop deeper voices. Boys should expect to experience this stage between 11 and 16 years old.
Girls' breasts continue to grow during this stage. Menstruation begins to occur, although periods do not happen regularly. The ovaries begin to release eggs six to nine months after the first period of menstruation. Girls go through this stage between 10 and 15 years old.
Tanner stage V, the final stage of puberty, allows boys to have adult physical characteristics, such as adult-sized genitals, and fully grown hair in all areas of the body. The boys have reached their final height, but muscle size and weight can vary depending on a boy's workout habits. Boys can reach this stage between 12 and 17 years old.
Girls also have adult bodies at this final stage. They have adult-sized breasts, uterus and genitals, and an adult pattern of body hair. Menstrual periods also become a regular occurrence. The girls typically approach this stage at 13 to 16 years old.