This research examined the validity of the theoretical model of reading outlined by the Simple View of Reading when measuring reading ability with a performance-based reading test. Participants were 95 fourth-grade, students randomly sampled from four schools in an urban district. The test we studied employed a mixture of traditional (multiple-choice) and performance assessment approaches (constructed-response items that required written responses). Our findings indicated that writing ability emerged as an important source of individual differences in explaining overall reading ability, even when we deconstructed the test into a multiple-choice-only score.