Flexi Says: The first signs of puberty appear at different times for different people. A boy might realize he's reached puberty when he starts needing to shave. A girl, on the other hand, starts getting her menstrual period during puberty. In boys, puberty begins when the pituitary gland tells the testes to secrete testosterone. Testosterone causes the following to happen: The penis and testes grow. The testes start making sperm. Pubic and facial hair grow. The shoulders broaden, and the voice becomes deeper. In girls, puberty begins when the pituitary gland tells the ovaries to secrete estrogen. Estrogen causes the following to happen: The uterus and ovaries grow. The ovaries start releasing eggs. The menstrual cycle begins. Pubic hair grows. The hips widen, and the breasts develop.