Mixed longitudinal data on the physical changes at puberty in 228 normal boys are presented together with normal standards for stages of genital and pubic hair development. The genitalia began to develop between the ages 9½ years and 13½ years in 95% of boys (mean = 11.6 ± 0.09) and reached maturity at ages varying between 13 and 17 (mean = 14.9 ± 1.10). The age at which pubic hair first appeared was not accurately determined, but its development through the later stages was studied. It reached the equivalent of an adult female distribution at a mean age of 15.2 ± 0.01 years. On average the genitalia reached the adult stage 3.0 years after they first began to develop; but some boys completed this development in as little as 1.8 years while others took as much as 4.7 years. Some boys complete the whole process in less time than others take to go from Stage G2 to Stage G3. The genitalia begin to develop before pubic hair is visible in photographs in practically all boys. The 41 boys in whom it could be studied reached their maximum rate of growth (peak height velocity) at a mean age of 14.1 ± 0.14 years. Very few boys (about 5%) reached peak height velocity before their genitalia were in Stage 4 and over 20% did not do so until their genitalia were adult. Peak height velocity is reached, on the average, nearly 2 years later in boys than in girls, but the boys9 genitalia begin to develop only about 6 months later than the girls9 breasts. Pubic hair appears about 1½ years later in boys than in girls.
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