Grammatical tense deficits in children with SLI and nonspecific language impairment: relationships with nonverbal IQ over time.

The relationship between children's language acquisition and their nonverbal intelligence has a long tradition of scientific inquiry. Current attention focuses on the use of nonverbal IQ level as an exclusionary criterion in the definition of specific language impairment (SLI). Grammatical tense deficits are known as a clinical marker of SLI, but the relationship with nonverbal intelligence below the normal range has not previously been systematically studied. This study documents the levels of grammatical tense acquisition (for third-person singular -s, regular and irregular past tense morphology) in a large, epidemiologically ascertained sample of kindergarten children that comprises 4 groups: 130 children with SLI, 100 children with nonspecific language impairments (NLI), 73 children with low cognitive levels but language within normal limits (LC), and 117 unaffected control children. The study also documents the longitudinal course of acquisition for the SLI and NLI children between the ages of 6 and 10 years. The LC group did not differ from the unaffected controls at kindergarten, showing a dissociation of nonverbal intelligence and grammatical tense marking, so that low levels of nonverbal intelligence did not necessarily yield low levels of grammatical tense. The NLI group's level of performance was lower than that of the SLI group and showed a greater delay in resolution of the overgeneralization phase of irregular past tense mastery, indicating qualitative differences in growth. Implications for clinical groupings for research and clinical purposes are discussed.