A longitudinal study of language acquisition in autistic and Down syndrome children.

The team watched the same kids talk every month for one to two years.

They matched autistic children with Down syndrome peers who used the same sentence length.

Then they tracked how grammar and vocabulary grew over time.

Once sentence length was equal, both groups added new words and grammar rules side by side.

Autistic kids did not lag behind; their language path looked typical.

Brignell et al. (2024) followed verbal autistic children up to age eleven and found the same thing: early language level, not the autism label, predicts later growth.

Koizumi et al. (2026) saw a different picture: Japanese children with autism or Down syndrome kept pace in vocabulary but fell behind in grammar when matched by mental age.

The clash is useful: H et al. matched by sentence length, while Manami matched by mental age. The first says grammar grows normally; the second says it needs extra help. Both can be true if you pick the right match.

Ferrari et al. (1991) used the same matched-group trick for daily living skills and showed autistic kids still struggle most with social use of those skills, reminding us that language progress does not guarantee social progress.

Stop assuming autistic grammar is broken. If a client’s sentences are short, work on length first; the grammar can catch up naturally. When you write goals, separate vocabulary size from syntax complexity and check which match you are using.