Both small-scale and epidemiological longitudinal studies of early language delay indicate that most late talkers attain language scores in the average range by age 5, 6, or 7. However, late talker groups typically obtain significantly lower scores than groups with typical language histories on most language measures into adolescence. These findings support a dimensional account of language delay, whereby late talkers and typically developing peers differ quantitatively on a hypothetical language ability spectrum. Variation in language ability is presumed to derive from variation in skills subserving language, such as auditory perception/processing, word retrieval, verbal working memory, motor planning, phonological discrimination, and grammatical rule learning. Expressive language screening at 18-35 months can serve an important public health function by identifying children whose expressive delay is secondary to autism spectrum disorder, intellectual disability, hearing impairment, receptive language delay, or demographic risk. Finally, the review suggests that demographic risk associated with low SES may become more important as a causal factor in language delay as children get older.
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