A study examined how specific developmental levels of cognitive ability affect the relationship between beliefs and performance; how cognitive development levels affect reading and writing performance; and how developmental level affects the interactions between the reading and writing domains. Subjects, 150 undergraduates between the ages of 18 and 23, were measured for cognitive developmental level, self-efficacy, causal attribution for reading and writing success and failure, outcome expectancy, locus of control, and reading and writing performance. Results indicated differences between developmental classification (concrete, transitional, formal) in the relationships between beliefs and reading or writing performance, and indicated changes in the regression models and the pattern of correlations between beliefs and reading or writing at the developmental level. Results further indicated differences between developmental classification in performance in reading and writing, and the relationship between reading and writing. Findings suggest that the specific cognitive skills represented by formal operational thinking influence both the magnitude of performance and beliefs and the structure of reading, writing, and belief relationships. (MM)