Quarrels between adolescents and their parents tend to signify a change to a more reciprocal adult relationship. Adolescence begins with puberty. During puberty, the sex organs mature and the individual becomes capable of reproduction. The pituitary gland mediates hormonal changes. In boys, the onset of nocturnal emissions and the growth of the testes, scrotum, and penis signify sexual maturity.
Children come to understand the principles of conservation.
This marks the beginning of abstract reasoning. Teenagers understand that ideas can be compared and classified, just as object can. They apply reasoning to situations they have not experienced firsthand. They can think about future possibilities and search systematically for answers to problems. Moral Development Piaget proposed that children's moral judgments build on their cognitive development.