During adolescence, the physical changes that occur due to puberty are completed. It is important for teens to practice good personal hygiene, eat well, exercise, and get enough sleep. An important part of adolescence is establishing a strong personal identity. During the teen years, peers become more important. Social and cultural influences affect moral development. Changes in the brain during adolescence enable teens to reason better and control impulses. In Piaget's stage of formal operations, teens become capable of abstract thought. Vygotsky believed that social interactions are essential for learning. Positive educational experiences contribute to intellectual growth.