Adolescents experience rapid rates of growth and maturation of the reproductive organs and glands. Together, these physical changes accomplish the biological task of transforming a child into an adult. Rapid change combined with wide variation among individuals tend to make adolescents extremely sensitive to their appearance. These physical changes also affect their social relations and emotions. That is why a pimple or being ahead or behind a classmate in physical growth can be so stressful to the teens' emotions.
Teens develop their abstract thinking capacities.
Before age 11 or 12 children think in terms of concrete objects and groups of objects. By age 16 most adolescents have gone from the simple way of thinking to complex forms of reasoning. They learn to approach a problem systematically. Moral issues become more complex because they understand that two sound rules or principles might conflict. They will struggle with a question about whether someone should report a friend for breaking a rule.