Piaget performed several experiments to study how children develop the concepts of conservation of volume and substance. In one experiment, he poured a specific amount of liquid into a tall beaker. Then he poured the same amount of liquid into a short and fat beaker. He asked the child which beaker had more liquid. Children in the pre-operational stage would insist that the tall and thin beaker had more liquid, although an older child could understand that both beakers have the same amount of liquid. In another experiment, the child is presented with two round balls of clay of the same size. In front of the child’s eyes, one ball of clay is rolled into a long, thin shape. When asked which is bigger, pre-operational children pointed to the long, thin one, even after witnessing it being formed out of the original round ball. These children could not conserve the volume or mass of the object as it was transformed. Piaget performed similar experiments to study conservation of number, quantity, and weight.