Final answer:
The concrete operational stage occurs between the ages of 7 to 11 years old. In this stage, children can think logically about real events, perform mathematical operations, and understand the concept of conservation.
Step-by-step explanation:
The concrete operational stage occurs between the ages of 7 to 11 years old in Piaget's theory of cognitive development. In this stage, children can think logically about real events and have a firm grasp on the use of numbers. They can perform mathematical operations, understand transformations, and master the concept of conservation. For example, they understand that even if something changes shape, its mass, volume, and number stay the same.