Vocabulary and Syntactic Development in Japanese Children With Autism Spectrum Disorder and Down Syndrome Accompanied by Intellectual Disability.

Manami and colleagues tested vocabulary and grammar in Japanese school-age children. They compared three groups: kids with autism, kids with Down syndrome, and typically developing peers matched for mental age.

The team used picture books, toys, and simple questions. They counted how many words each child knew. They also checked if the child could understand and use correct word order and endings.

All three groups knew about the same number of words. Vocabulary size lined up with mental age for every child.

Grammar told a different story. Both the autism and Down groups made far more word-order and ending errors. They also had trouble understanding complex sentences, even though their word knowledge was equal.

Charlop et al. (1990) tracked English-speaking toddlers for two years and saw vocabulary and grammar grow together once sentence length was matched. The new Japanese data agree that vocabulary keeps pace with mental age, but they add a twist: grammar lags behind even when words do not.

Giallo et al. (2014) showed that reading comprehension in autism hinges on vocabulary size. Manami’s team extends that idea by showing vocabulary is not enough; syntax must be taught directly.

Järvinen-Pasley et al. (2008) found autistic children fail sentence-level prosody tasks while passing single-word ones. The same sentence-level weakness now shows up in grammar, strengthening the case for targeting whole-sentence skills.

Do not assume a big vocabulary means strong grammar. When you write goals, add separate syntax targets such as correct past-tense endings or question word order. Use visual sentence strips and modeled dialogues during play and daily routines. Check comprehension of multi-step directions, not just single words. These simple shifts can close the grammar gap that vocabulary scores hide.