Boys and girls grow about 5 centimeters per year in height before puberty, and after entering puberty, children’s growth rate will enter a period of sudden leaps and bounds there are great changes. Girls grow faster when their breasts begin to develop, and the fastest growth in height occurs about one year after breast development. the average time from the beginning of breast development to full maturity is 3 years. usually the fastest growth in height for a girl is at the age of 11-13 years, and the fastest growth in height in that year can be 7-9 centimeters, with an average increase in height of 20 in 3 years. menstruation usually occurs 18 months after rapid growth, with an average age of Menstruation usually occurs 18 months after rapid growth, at a mean age of 13.25 years, with a maximum range of ±1.5 years. 10% of girls have their first menstrual period before age 12, and 10% after age 15, with the average menstrual period beginning about 2 years after the onset of puberty. When menstruation occurs, the period of rapid growth is over and growth rates begin to decline, signaling that the children’s growth is nearly complete. In boys, the testes do not begin to grow rapidly until they reach 10 milliliters in size, and testicular enlargement to 4 milliliters is usually considered the onset of puberty in boys, with other secondary sexual characteristics such as pubic and axillary hair appearing successively. The height surge occurs at a later stage of genital and pubic hair development, with beard and body hair appearing later in puberty. The average age of onset of the pubertal surge in boys is 12.5 years, and the average age of fastest growth is about 14 years, for a total of 28 centimeters. Usually the beard grows to the point where it needs to be shaved, indicating late puberty and approaching final height.