This study compared an expert-based cognitive model of domain mastery with student-based cognitive models of task performance for Integrated Algebra. Interpretations of student test results are limited by experts' hypotheses of how students interact with the items. In reality, the cognitive processes that students use to solve each item may be very different than those assumed by the test developers. Without knowledge of how students are actually operating on these test items and the cognitive processes they use, interpretations from the results of the examination may be compromised. In this study, I investigated the cognitive processes that students used when solving nine multiple-choice integrated algebra items from a large-scale examination. Once elicited and recorded through think-aloud protocols, the students' cognitive processes were synthesized into item-level cognitive models of task performance and these models were compared with the less specific expert-based cognitive model of domain mastery currently used to develop the examination. As the level of agreement between these two was very high, this comparison provided evidence for the validation of inferences from test scores. The utility of this information for validation and the implications for test development and score reporting are discussed. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]