Two measures of syntactic complexity, clauses per T-unit and words per clause, were used to examine differences among four genres of text--narrative, descriptive, compare/contrast, and persuasive--written by the same two cohorts (83 students in grades three and five and 96 students in grades five and seven) on two occasions 2 years apart as part of a larger longitudinal study. For clauses per T-unit, a measure of subordination, significant differences were found between persuasive essays, which had more subordinate clauses, and the other three genres. For words per clause, an indicator of the denser syntax of the academic register, significant differences were found between descriptive texts, which had more words per clause than the persuasive essays, which did not differ from the compare/contrast texts. Over the grade levels studied, the measures of syntactic complexity did not increase in their differentiation among the four genres. The two measures of syntactic complexity were negatively correlated, especially for the persuasive essays. For text length, which is thought to reflect compositional fluency, grade, genre, and grade x genre effects were significant for both cohorts. Post hoc analyses found few examples of the syntax-level structures characteristic of the academic register. These findings suggest that although students could produce each kind of genre, their ability to do so may have been compromised by their limited knowledge of the syntactic structures required to achieve text-level genre goals. Researchers and educators should consider the syntactic- and text-level requirements for different school-based genres in designing and evaluating writing instruction.