Associations between syntax and the lexicon among children with or without ASD and language impairment.

Syriopoulou-Delli et al. (2012) looked at how grammar and word knowledge link up in kids with autism. They compared four groups: ASD with good grammar, ASD with grammar trouble, kids with specific language impairment (SLI), and typical kids.

The team gave vocabulary depth tests and grammar tests. They wanted to see if weak grammar in ASD creates the same sparse word webs seen in SLI.

Kids who had ASD but solid grammar also had age-appropriate word knowledge. When ASD and grammar problems occurred together, the children's lexicons looked just like those of SLI peers—thin and poorly connected.

The data show a tight syntax-lexicon tie: grammar weakness, not the autism label, predicts shallow vocabulary.

Dai et al. (2025) extends these results to Mandarin. They found that ASD plus language impairment (ALI) hits complex receptive syntax harder than SLI, especially on which-questions. Together the studies tell us to probe both word knowledge and sentence understanding.

McGonigle-Chalmers et al. (2013) seems to disagree at first—they showed non-verbal ASD kids grasping grammar on a touch screen. But the kids in that study had good receptive syntax; their bottleneck was speech output, not grammar. The papers line up once you separate receptive grammar from expressive speech.

Root et al. (2017) adds brain evidence: weaker language in preschool boys with ASD maps to altered white-matter in the inferior longitudinal fasciculus. Behavior and biology both point to a grammar-lexicon highway that can break down.

If you test only vocabulary or only syntax you can miss half the picture. Run quick probes for both domains, even in kids who talk a lot. When grammar is weak, expect sparse word networks and plan intervention targets that link new words to sentence frames. This one change can sharpen your assessment and save therapy time.