The Concrete Operational stage is the third phase in Jean Piaget's theory of cognitive development, typically occurring between ages 7 and 11. During this stage, children begin to think logically about concrete events and understand the concept of conservation, which means they can recognize that quantity doesn't change even when its shape does. Children in the Concrete Operational stage also develop skills in classification and seriation, allowing them to organize objects based on different attributes. They can solve problems in a more systematic way but still struggle with abstract or hypothetical concepts, which are better understood in later stages of development.