Purpose: As children develop skills in writing across academic contexts, clinicians and educators need to have a fundamental understanding of typical writing development as well as valid and reliable assessment methods. The purpose of this study was to examine the progression of linguistic elements in school-age children's narrative and expository writing development. Method: Narrative and expository writing samples produced by 89 children in Grades 2 through 4 were analyzed at the microstructure and macrostructure levels. Measures of receptive vocabulary, wordlevel reading, and reading comprehension were obtained. Results: Exploratory factor analyses revealed 4 microstructure factors (e.g., productivity, grammatical complexity, grammatical accuracy, and lexical density) and 1 macrostructure factor (e.g., a combination of organization, text structure, and cohesion). Multivariate analyses of covariance with reading comprehension as a covariate showed that productivity and macrostructure were sensitive to grade-level and genre differences and that expository grammatical complexity was sensitive to grade-level differences. Conclusions: Findings are discussed in light of grade-level standards for narrative and expository writing and current practices in writing assessment. Multiple suggestions are offered for clinical and educational implications, and specific directions are provided for future research.