Children aged between two and 10 years were assessed on a new reception of syntax test (ROST). Validations of the test are reported for monolingual fluent control children under five (by examining the relationship with mean length of utterance and the Oxford Communication Development Inventory) and for over fives (relationship with a new judgement of grammaticality test using syntactic categories common to the two tests). Performance of these children was compared with performance of children who stutter and children with English as an additional language. In this study, the test was divided into under-five and over-five forms. Any young child progressing to the over-five syntactic categories, or any older child doing the under-five syntactic categories was dropped from the analysis. ROST scores prepared according to this scheme led to no differences between the control and either of the subject groups tested. However, compared to controls, the children with English as an additional language (but not children who stutter) had a significantly higher proportion of children above five who did the under-five categories (and were, therefore, excluded from the analyses). The higher proportion of children who did the under-five syntactic categories in the English as an additional language group indicates that group scores would have been lower if their syntax results had been included in the analysis. Further analyses provided some evidence that two groups with English as an additional language (Turkish and Cantonese speakers) did not perform any better on selected syntactic categories in their native language compared with their performance in English.