Purpose: The primary aims of this study were to: (1) to describe average change in the writing quality of fifth grade students from the fall and spring of the school year; (2) examine relations between linguistic features and writing quality rating; and (3) test for differential growth between groups of students who differ in linguistic and ability backgrounds. Method: Participants included 1,396 students in fifth grade. Writing quality was assessed using a 10 point rating rubric. Three microstructural measures were included: number of different words (NDW), academic word use, and use of advanced connectives. Results: Significant increases in writing quality were evidenced from fall to spring. Quality ratings were significantly related to linguistic features including lexical diversity, use of academic words and advanced connectives. Additionally, results from a two-level hierarchical linear model with students nested within classrooms indicated that there was a significant interaction between free/reduced lunch eligibility and initial performance in predicting the change in quality from fall to spring. After taking initial writing quality into account, English proficiency and the presence of language-based exceptionalities were significant predictors of students' gains in writing quality across the school year. Conclusions and implications: Quality ratings are sensitive to change across a school year. Findings highlight differentiated writing growth based on linguistic and socioeconomic backgrounds. Findings point to the need for causal research examining mechanisms to improve students' overall writing quality outcomes.