The relationship between mean length of utterance (MLU), Persian developmental sentence score (PDSS), and photographic expressive Persian grammar test (PEGT) in typically developing children and those with developmental language disorder (DLD).

Purpose: This study investigated the relationship between three practical measures for evaluating Persian grammar expression skills, MLU, PDSS, and PEGT, in preschool children with developmental language disorder (DLD) and their typically developing (TD) peers.

Method: Secondary data were obtained by re-analyzing language samples collected in previous studies. Previously audiotaped language samples of 25 monolingual 5-7 years-old Persian children with DLD and 25 TD children were transcribed and reanalyzed to calculate MLU in words (MLU-w) and PDSS for comparison with the results of PEGT.

Results: Children with DLD had lower scores in PEGT, PDSS, and MLU-w than TD children (p < 0.001). In addition, there was a strong correlation between PDSS and MLU-w in both DLD (r = 0.91) and TD groups (r = 0.79). There was a significant correlation between PEGT and MLU (r = 0.76) and PDSS (r = 0.78) in the DLD group, while these correlations were not significant in TD group.

Conclusions: Considering the positive and significant correlation between MLU, PDSS, and PEGT in children with DLD, the use of PEGT, as a valid, reliable, and accurate test of grammar, which can be implemented quickly and easily, is suggested for clinical purposes of identification and screening of Persian children with DLD.