Final answer:
Conservation is a cognitive skill where a child understands that one property of an object can change while the other property remains the same. For example, pouring water from one glass to another does not change the amount of water. This concept is important in understanding cognitive development in children.
Step-by-step explanation:
A cognitive skill where a child understands that even though one property of an object changes, the other property still remains the same is called conservation. Conservation is a concept in cognitive development that involves the understanding that certain properties of objects, such as volume or quantity, are not changed by superficial transformations, such as changes in shape or arrangement. For example, a child who understands conservation would know that pouring water from a short, fat glass into a tall, skinny glass does not change the amount of water.