Specific language impairment (SLI) and autism spectrum disorders (ASD) are complex highly heritable disorders that involve primary impairments in language and communication. A subtype of ASD includes impairments in language that parallel those found in SLI, including two core clinical markers for SLI: deficits in phonological working memory, as measured on nonword repetition tasks, and deficits in grammatical morphology, particularly in marking tense on verbs. The goal of this project is to investigate the brain bases of these two core deficits in SLI, ASD, and typical development of these core language abilities. Aim 1 will investigate the neural basis of phonological working memory (nonword discrimination) and grammaticality judgments in 96 typically developing children aged 5-12. For the nonword discrimination task, we predict that increases in nonword length will result in greater recruitment of bilateral superior temporal gyrus (STG) and left inferior frontal gyrus (LIFG), with developmental changes primarily in LIFG. In the grammaticality judgment task we predict that errors involving omission of obligatory tense (e.g., past tense -ed) will lead to greater activation in LIFG and left STG, compared to correct sentences. Aim 2 will implement the same experimental paradigms in 48 children with SLI and 96 children with ASD (48 with and 48 without co-morbid language impairment) aged 8-12 years old, who will be compared to age- and language-matched typical controls. We predict that in children with SLI the degree of functional connectivity between IFG and STG will be reduced and that functional activation in STG and/or LIFG and functional connectivity between these regions will correlate with behavioral performance in both experiments. We also predict that the ASD children with language impairment will show similar atypical activation patterns as in the SLI group and that over time, both groups will show activation patterns that more closely resemble the typical children. This is the first developmental study on the neurobiological bases of core impairments in language in SLI and ASD. The findings will pave the way to identifying potential biomarkers for these disorders and will open up the possibility of providing intensive interventions for school-aged children that are individually tailored to biomarker profiles.