An interactive Flash diagram of puberty in boys, a child’s physical transition to sexual maturity. This transition may last for several years, during which the gonads (testes) grow, develop, and (along with the pituitary and adrenal glands) release hormones that cause other physical changes—usually starting between ages 9 and 14 in boys. A boy undergoes numerous physical changes during puberty, including growth of the testes, scrotum, and penis. His testes mature and begin to produce sperm. His body size and shape change, and he develops facial and body hair. The Tanner scale is often used to assess a child’s sexual development, having five stages each associated with a cluster of physical characteristics—click through the slides to learn about how the male body develops at each stage.