Final answer:
In Jean Piaget's theory, individuals entering adolescence begin the formal operational stage, characterized by abstract thought and hypothetical reasoning beginning around age 11.
Step-by-step explanation:
According to Jean Piaget's theory of cognitive development, individuals going into adolescence enter the formal operational stage. This stage generally begins around the age of 11 and continues into adulthood. During the formal operational stage, adolescents develop the ability to think abstractly and to understand hypothetical concepts. They become capable of higher-level thinking processes including logical reasoning, contemplating multiple perspectives, and envisioning hypothetical scenarios. Contrary to younger children who think more concretely, adolescents and adults can use abstract thinking to problem-solve, consider alternative solutions, and test these ideas in their minds.