According to Jean Piaget, children in formal operational stage

Piaget's formal operational stage (beginning around age 11) is characterized by the ability to think abstractly, reason hypothetically, and use propositional logic. Children at this stage can formulate hypotheses and systematically test them—a process called hypothetico-deductive reasoning. Centration and irreversibility are features of the preoperational stage. Inability to conserve, classify, and seriate is also typical of preoperational thinkers. Make-believe and symbolic play emerge in the preoperational stage, not the formal operational stage.