The primary objective of this study was to compare the syntactic complexity of informational texts produced by fifth-grade students (a) with and without language impairment and (b) with and without native English-speaking proficiency on a curriculum-based reading and writing task. Expository writing samples produced by 114 children enrolled in the fifth grade were analyzed at the utterance level for five features of complex syntax, including the frequency of utterances containing complex syntax and specific clause types (conjoined, subordinate, relative, full complement). For each of the four groups, we report frequency counts, means, standard deviations, and ranges of performance across the five syntax measures. Multivariate analysis of variance revealed there were significant group differences on measures. Specifically, children with typical language development, regardless of English proficiency level, wrote more words, utterances, and different word roots than their peers with language impairment. When productivity (i.e., text length) in the writing samples was controlled, multivariate analysis of variance revealed there was a significant difference between groups in use of relative clauses, but not for the use of conjoined, subordinate, or full complement clauses. In particular, English proficient students with language impairment produced a greater proportion of utterances with relative clauses. A post hoc correlation analysis showed moderate, positive correlations among writing cohesion and variables of complex syntax. We consider multiple implications for clinical practice and further research.