In this study, the effects of writing ability and mode of discourse of cognitive capacity engagement were investigated. Sixty-three college freshmen of varying writing abilities (basic, average, and honors) were randomly assigned to experimental treatments (descriptive writing, narrative writing, and persuasive writing). Using the secondary task method, it was found that writing ability differentially affects cognitive capacity engagement across modes. For example, honors writers were least engaged when writing descriptive essays but were most engaged when writing persuasive essays whereas average writers were most engaged when writing descriptive essays but were least engaged when writing narrative essays. Analytic quality scores and engagement were related and results were interpreted in the context of schema theory to estimate the learning potential of a given mode of discourse. Also, engagement and syntactic complexity treasures were related. It was found that as words per clause increased, engagement also increased; whereas, as clauses per T-unit increased, engagement decreased.