Developing discursive competence in informational writing during K-12 education is an important preparation for academic writing in college and beyond. This study examines school children's use of nouns—a powerful grammatical resource for making meaning in academic and disciplinary contexts—in informational writing. Approximately 200 students in third, fifth, seventh, and ninth grades were asked to write an informational text on a familiar topic of interest. The writing corpus was first coded for presence of nouns and for holistic quality. These nouns were then analyzed for their lexical, syntactic, and semantic complexities. Statistical analyses yielded the following results: (a) the children scored low on all measures of nominal complexities; (b) there was a clear developmental trend toward greater nominal complexities across grades; (c) older children scored higher on holistic rating and used a higher percentage of complex nouns than did younger children, although both relied heavily on nouns without any modification or nouns with only one premodifier; and (d) nominal complexity measures significantly predicted the holistic quality of informational writing. These results were interpreted in light of the research literature on language/literacy learning and the research context of the present study. Their implications for academic writing research and instruction were also discussed.