["Autism Research, Volume 19, Issue 4, April 2026. ", "\nABSTRACT\nPast research has revealed large differences between typically developing (TD) and autistic children's language development. However, little is known about whether such differences are quantitative or qualitative, especially in the morphosyntactic domain. This study is the first longitudinal research aiming to systematically investigate the developmental patterns of a wide range of Mandarin grammatical markers in autistic children. The mastery of target markers in autistic children (N = 88, Mage = 44.9 m, Range = 26–76 m) was assessed longitudinally across three time points using parent reports and compared with that of TD children (N = 84, Mage = 23.2 m, Range = 16–30 m) assessed at a single time point. We further examined the influence of autism severity and initial language ability. The results suggested that autistic children acquired Mandarin grammatical markers in a typical sequence but at a slower rate. Additionally, this developmental pattern was maintained regardless of autism severity and initial language ability. These findings suggest that autistic children's language development differs quantitatively but not qualitatively from that of TD children, reflecting developmental delay rather than deviance.\n"]