MOCCA-C is an assessment of adult reading ability designed for early diagnosis of reading problems, for formative assessment in reading intervention planning, for assessment of reading improvement over time, and for assessment of reading intervention outcomes. It uses both narrative and expository reading passages and it currently has four forms. Two goals of this research were to compare narrative and expository passages on (a) their difficulty and (b) their ability to discriminate between good and poor readers. An additional goal was to assess whether narrative and expository passages measure the same or different comprehension dimensions. A final goal was to assess the reliability of forms. We randomly assigned students to forms with between 274 - 279 college students per form. Across the several forms, results suggest that narrative passages are easier and better discriminate between good and poor readers. However, both narrative and expository passages measure a single dimension of ability. MOCCA-C scores are reliable. Implications for research and practice are discussed.