Language impairment in a child with Down syndrome is often determined by comparing performance on standardized language tests with the child's mental age rather than with chronological age. Why can mental age legitimately be used as a performance criterion?

• A. Using chronological age would overidentify language disorders
• B. Using chronological age would underidentify language disorders
• C. Mental age always correlates with verbal performance
• D. Language performance is expected to exceed mental age

Answer: (D)

Language development is best interpreted in the context of a child’s overall cognitive level. In Down syndrome, there can be a general delay, but language abilities often progress in relation to that cognitive level rather than strictly to chronological age. Therefore, using mental age as the benchmark helps identify a language difficulty that is disproportionate to the child’s cognitive development, rather than just reflecting a global delay. If language performance is expected to exceed the mental-age level and it does not, that gap signals a legitimate language impairment beyond what would be predicted by cognitive development alone. This is why mental age can be a meaningful performance criterion.