During adolescence there is a maturing of the sexual reproductive organs. The rate of change and maturation is different for everyone. Both boys and girls reach their adult height and weight during this period of change with growth spurts for boys occurring between the ages of 13 and 18 years, and for girls between 11 and 13 ½ years.

The onset of puberty occurs from the ages of 9 to 12. For girls, this begins with the secretion of oestrogen. This leads to the development of the breasts, underarm and pubic hair and menarche (the start of periods) - which usually happens approximately two years after breast enlargement.

For boys, sexual development begins with the secretion of testosterone. This causes changes in the reproductive organs with enlargement of the scrotum and testes, and then growth of the penis. This is followed by the growth of the seminal vesicles and the prostate gland, and the development of underarm, pubic hair and facial hair.