Final answer:
A child in the concrete operational stage can reason about concrete realities and understand concepts such as conservation and mathematical transformations. They recognize that the appearance of an object can change without altering its quantity.
Step-by-step explanation:
A child in the concrete operational stage of cognitive development would be able to reason about concrete events, mathematics, and physical changes in objects, and comprehend conservation. This developmental stage, defined by Jean Piaget, occurs from roughly ages 7 to 11. In this period, children grasp the concept that the quantity of an object doesn't change even if its appearance does. For example, they would understand that water in different-shaped glasses has the same volume, and they would recognize that mathematical operations can reverse, such as addition relating to subtraction, and multiplication to division. Consider the case of two siblings, Keiko and Kenny, who are given pizza slices. Kenny, who is likely in the preoperational stage, thinks he has more simply because his slice is cut into more pieces. Keiko, in the concrete operational stage, knows that the amount of pizza is equal despite the number of pieces, demonstrating an understanding of conservation.