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Physical development
Adolescence is often considered to begin with puberty, the appearance of mature sexual characteristics. In girls this is marked by menarche, the onset of menstruation. The average age is about 12^1/2 years , but the normal range is of growth in height and weight begins to increase, reaching a peak about a year before the menarche. The peak rate is the most rapid growth in the postnatal period. Because of its timing, this period of rapid growth is sometimes called the preadolescent growth spurt.
In boys there is no striking change analogous to the menarche to mark the beginning of adolescence. However, a growth spurt in height and weight occurs, and its pattern is about the same as in girls except that it is about two years later. Thus, adolescence begins about two years later in boys than in girls.
Like girls, boys vary widely in the age at which puberty begins. However, the “average” early-maturing boy begins puberty at about the average normal age for the beginning of puberty in girls. Similarly, the “average” late-maturing girl begins puberty at about the average normal age for boys. Research shows such individuals have few problems in learning to adjust to the opposite sex. The early-maturing boy has the better time of it, though, because he is also a hero to the normally-maturing boys, while the late-maturing girl is not well accepted by normally-maturing girls. In contrast, the early-maturing girl is too far ahead of her classmates of both sexes, and the late-maturing boy too far behind. Both have adjustment problems.
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