Students’ proficiency in constructing sentences impacts the writing process and writing products. Linguistic demands in writing differ in terms of both student characteristics and measurement features. To identify various syntactic demands considering these features, we conducted a meta-analysis examining the relationships between syntactic features (complexity and accuracy) and writing performance (quality, productivity, and fluency) and moderating effects of both student characteristics and measurement features. A total of 109 studies (effect sizes: 871; the total number of participants: 24,628) met the inclusion criteria. Results showed that there was a weak relationship for syntactic accuracy (r = .25) and complexity (r = .16). Writers' characteristics, including grade level and language proficiency, and measurement features, writing genres, writing outcomes, whether the writing task is text-based or not, and type of syntactic complexity measures, were significant moderators for certain syntactic features. The findings highlighted the importance of writer and measurement factors when considering the relationships between linguistic features in writing and writing performance. Implications were discussed regarding the selection of syntactic features in assessing language use in writing, gaps in the literature, and significance for writing instruction and assessment. • Aimed to depict the relationships between syntactic features and writing performance. • Found weak relationships between syntactic features and writing outcomes. • Relationships vary as a function of student characteristics and measurement features. • Noun phrase complexity might be more valid than some traditional syntactic complexity measures. • Findings have important implications for writing assessments.