The purpose of this study was to explore relationships between language variables and writing outcomes with linguistically diverse students in grades 3-5. The participants were 197 children from three schools in one district in the mid-Atlantic United States. We assessed students' vocabulary knowledge and morphological and syntactical skill as well as narrative writing ability in the spring of the academic year. The importance of language skills was investigated in two separate sets of models predicting contextual conventions and story composition. Controlling for grade level, language status, and transcription skills, syntactical skill was related to contextual conventions. Additionally, the relationship between syntactical skill and contextual conventions differed for ELs and non-ELs such that at higher levels of syntactic skill non-ELs showed better performance in contextual conventions. There was also a relationship between vocabulary breadth and story composition. Controlling for vocabulary breadth, ELs performed better than non-ELs on the story composition task.