Background: Developmental Sentence Scoring (DSS) was developed as a numerical measurement and a clinical method based on the morphosyntactic acquisition in the English language. The aim of this study was to develop a new numerical tool similar to DSS to assess the morphosyntactic abilities in Persian-speaking children. Methods: In this cross-sectional and comparative study, the language samples of 115 typically developing Persian-speaking children aged 30 - 65 months were audio recorded during the free play and picture description sessions. The Persian Developmental Sentence Score (PDSS) and the Mean Length of Utterance (MLU) were calculated. Pearson correlation and one - way Analysis of variance (ANOVA) were used for data analysis. Results: The correlation between PDSS and MLU in morphemes (convergent validity) was significant with a correlation coefficient of 0.97 (p < 0.001). The value Cronbach's Alpha (α= 0.79) in the grammatical categories and the split-half coefficient (0.86) indicated acceptable internal consistency reliability. Conclusion: The PDSS could be used as a reliable numerical measurement to estimate the syntactic development in Persian-speaking children
