Dr. Jean Piaget gave 5-year-old children two identical glass beakers, each containing the same amount of liquid. The children had no difficultly understanding that the amount of liquid was the same in both containers. However, when the liquid from one beaker was poured into a tall, thin beaker, the children mistakenly believed that the taller glass had more liquid. This finding shows which characteristic of children in the Pre-Operational Stage of Development.