Passage: A developmental psychologist notes that children progress through an ordered sequence of stages. In one task, a child watches as water is poured from a short, wide glass into a tall, narrow glass. A child around age four insists the tall glass 'has more,' while an eight-year-old recognizes the amount is unchanged. The understanding that quantity remains the same despite appearance changes is termed conservation. Younger children fail this task due to centration—the tendency to focus on only one salient feature, like height, while ignoring others.