Morphosyntactic and lexical features in 5;0-6;0 years old Persian-speaking children with a history of late-talking: A 3 years follow up.

This longitudinal study compared morphosyntactic and lexical skills in Persian-speaking children aged 5;0-6;0 with a history of late-talking (LT, n=28) and typically developing peers (TD, n=26). Participants, initially assessed at 30 months (31 LT, 32 TD), were matched for age and socioeconomic status. Language skills were evaluated using the Test of Language Development (TOLD), mean length of utterance in morphemes (MLUm), Persian developmental sentence scoring (PDSS), a² (Maas), number of total words (NTW), and number of different words (NDW). Results showed that 10 LT children improved (classified as improved LTs) but still scored below TD peers. Improved LTs outperformed unimproved LTs. TD children significantly surpassed both LT groups in morphosyntactic and lexical measures. Stepwise linear regression identified expressive vocabulary size (MCDI-II: Words) and NDW at 30 months as significant predictors of later MLUm and PDSS scores in the combined sample (LT+TD) at 5;0-6;0 years. Despite compensatory progress, LT children remained at the lower end of the normal range, underscoring the need for ongoing monitoring and early intervention during critical developmental periods. Smaller expressive vocabularies at 30 months correlated with persistent delays, highlighting the importance of targeted support for high-risk cases.