Final answer:
The experiment of pouring water between a short, wide glass and a tall, thin glass tests children's comprehension of volume conservation during the concrete operational stage.
Step-by-step explanation:
Pouring water from a short, wide glass into a tall, thin glass is commonly used as a test to assess children's understanding of the concept of volume conservation. This cognitive ability typically develops during the concrete operational stage of cognitive development, between the ages of 7 and 11 years old. At this stage, children begin to grasp that the amount of liquid, or its volume, remains constant despite changes in its container's shape. They also learn about the principle of reversibility, meaning that a changed object can return to its original state, such as water being poured back and forth between glasses without changing its volume, aside from minimal losses due to spillage.