The best way to determine the arrival of puberty is to note the physical changes that occur. These changes are referred to as the sexual maturity rating, or Tanner stages, named after the physician who detailed the order in which the changes typically occur. The sequence of the changes may be different, but they will all eventually take place.
For girls, puberty usually begins between the ages of eight and 13; typically, the first sign is breast development. This is soon followed by the growth of pubic hair and then armpit hair. The menstrual period generally begins a couple years after those changes, and regular ovulation cycles occur soon thereafter. Although this is the usual order of the signs of puberty occurring, some girls develop pubic hair before their breasts begin to grow.
For boys, puberty usually begins between the ages of nine and 14; an increase in the size of their testicles is normally the first sign. This stage lasts for about six months and is followed by an increase in penis size. Pubic and armpit hair then begin to grow. The voice then deepens and muscles grow bigger. The growth of facial hair is usually the last visible sign of puberty. Production of sperm occurs near the start of puberty.