This study analyzes the instantiation aspect of the experiential metafunction of students’ writings in order to understand students’ language and its implications for language development. The framework for understanding is transitivity profiling, a quantitative method examining the frequency of occurrence of transitivity choices made in students’ writing. Evidently, in each expository, opinion, and emotional writing, we find significant differences in the frequency of process types and participant patterns used by elementary, middle, and high school students. Based on these result, we suggest that (1) students’ language developmental aspect is different depending on the genre, (2) a significant difference in patterns of participants by school level is concentrated in a combination of core participants, and, (3) as the school level increases, the ellipsis of core participants increases significantly.