The adolescent transition of puberty is marked by majors biological and social challenges. This transitional phase lasts about five years, from approximately 9 years to 14 years old. Girls tend to experience the transition a bit earlier than boys - by approximately 10 to 12 months. Both sexes experience an increase in weight and height. In girls, the first menstrual cycle occurs near the end of puberty, with the ability to bear children occuring a few years thereafter. Boys experience increased production of testosterone and other male sex hormones. The timing of these biological changes can have important consequences to an adolescent's social development. Boys who mature early generally have more self-confidence than their late-blooming counterparts. Conversely, girls who mature early often feel shy and self-conscious about their bodies.