Objectives: Word definitional skills [WDSs] were classified according to the quality of both semantic content and syntactic form. The aim of the present study was to investigate the syntactic development in WDSs in typically developing school- age children. Methods: In this cross-sectional and descriptive- analytical study, 150 of typically developing schoolage children participated by the multistage sampling method in the second to sixth grade from primary schools in 1, 7 and 17 municipal districts of Tehran. The definition skill was assessed with word definition task. The reliability was assessed by two independent values and the validity was determined by the content. The results were analyzed by the SPSS [22th version] statistical software and with the method of independent- samples T test, univariate analysis of variance and Tukey test.
Results: The form analysis revealed that all children use phrase/clause or simple sentence, transitional form and Aristotelian form frequently, but by increasing the age, definitions were developed from simple syntactic structure into Aristotelian form, in fact mean score of the form in word definition was significantly increased by age [p< 0.001] .