Language immersion programs seek to develop multilingual, multiliterate individuals able to engage with academic content. Studies of immersion students' language development provide details regarding language proficiency and accuracy, yet they generally do not address how features of written, academic language, for example, syntactic and lexical complexity, develop. To this end, this study seeks to understand if and how the syntactic complexity of written texts produced by middle school Spanish immersion students differs across grades. It examines discipline-related, persuasive texts written by 186 Grade 6-8 Spanish immersion students from five programs, analyzing syntactic complexity at the phrasal, clausal, and supraclausal levels and considering both length-based and subordination measures. Findings suggest that syntactic complexity does not change significantly in middle school for immersion students unlike findings with nonimmersion students. Explanations for and implications of the findings are explored.