George thinks his teacher is joking when she tells him that she has a son who is his age. According to Piaget's theory of cognitive development, which concept is George having trouble with?

Answer:The concept of classification or hierarchical classification.

Explanation:Piaget believes children only gains the ability to understand the concept of conservation and classification at the age of 7 to 10.

Below this age children rarely understand the concept of hierarchical classification which refers to being able to understand that things can be sorted into more specific groups based on their shared similarities such as same age, size and shape.