Robert's mother pours a cup of milk for him and then realizes that the cup has a small chip in the rim. Not wanting her son to cut his lip, she pours the milk into another cup. The second cup happens to be shorter and wider than the first cup

Robert is upset because he thinks that he has less milk. Explain Robert's behavior using your knowledge of Piaget's stages of cognitive development.
What will be an ideal response?

A good answer will be similar to the following:
+ Robert is in the preoperational stage of cognitive development (between 2 and 7 years of age).
+ Preoperational children often concentrate on one aspect of a problem, but totally ignore other, equally relevant aspects (centration). Piaget demonstrated centration in experiments involving conservation.
o Robert is centered in this thinking. Robert believes that he has less milk than before because the milk is lower than it was before it was poured. He ignores the fact that the change in the level of the milk is always accompanied by a change in the diameter of the cup.