Which cognitive ability allows children to understand that two sets can represent the same quantity?

The correct answer is conservation, which is a key cognitive ability that emerges during the concrete operational stage of development, as described by Jean Piaget. Conservation refers to the understanding that certain properties of objects, such as volume, mass, or number, remain the same even when their form or arrangement changes. This ability allows children to recognize that two sets of objects can be equivalent in quantity despite differences in appearance.

For example, if you have two sets of marbles and spread one set out in a wider line while keeping the other set closer together, a child who understands conservation will acknowledge that both sets still have the same number of marbles, even if they look different. This cognitive skill is crucial for children's mathematical reasoning and logical thinking, allowing them to grasp more complex concepts later on.

The other options do not correctly describe this specific ability. Classification involves the ability to group objects based on shared characteristics but does not pertain to understanding equivalent quantities. Egocentrism refers to a child's inability to see perspectives other than their own and is typical in the preoperational stage. Assessment, although important in evaluating cognitive skills, is not a developmental concept related to understanding quantity.