Until the maturation of their reproductive capabilities, the pre-pubertal physical differences between boys and girls are the external sex organs.
On average, girls begin puberty around ages 10–11; boys around ages 11–12.
Puberty which starts earlier than usual is known as precocious puberty.
Puberty is the process of physical changes through which a child's body matures into an adult body capable of sexual reproduction.
It is initiated by hormonal signals from the brain to the gonads: the ovaries in a girl, the testes in a boy.
In response to the signals, the gonads produce hormones that stimulate libido and the growth, function, and transformation of the brain, bones, muscle, blood, skin, hair, breasts, and sex organs.
Physical growth—height and weight—accelerates in the first half of puberty and is completed when an adult body has been developed.
The conversion of testosterone to estradiol depends on the amount of body fat and estradiol levels in boys are typically much lower than in girls.
The male "growth spurt" also begins later, accelerates more slowly, and lasts longer before the epiphyses fuse.
Although boys are on average 2 centimetres (0.8 in) shorter than girls before puberty begins, adult men are on average about 13 centimetres (5.1 in) taller than women.
Notable among the morphologic changes in size, shape, composition, and functioning of the pubertal body, is the development of secondary sex characteristics, the "filling in" of the child's body; from girl to woman, from boy to man.
Derived from the Latin puberatum (age of maturity), the word puberty describes the physical changes to sexual maturation, not the psychosocial and cultural maturation denoted by the term adolescent development in Western culture, wherein adolescence is the period of mental transition from childhood to adulthood, which overlaps much of the body's period of puberty.