The main focus of this study is to determine the effect of test design on the academic performance of students with disabilities participating in the NCEXTEND2 modified assessment program during the 2010-2011 school year. Participation of all students in state and federal accountability measure is required by No Child Left Behind (2001) and the Individuals with Disabilities Education Improvement Act (2004). Currently, states have several assessment options for testing students with disabilities; however, it is presumed that the next reauthorization of the Elementary and Secondary Education Act will no longer allow the provision of the AA-MAS (Bradshaw, 2010). Thus, more research is needed to determine how students currently participating on the AA-MAS would perform on the general education assessment. An experimental research design was used in this study consisting of a control group data set containing test scores from tests with three response options and an experimental group data set containing test scores from tests with four response options. This archived, quantitative data was used to conduct two-sample z-tests to investigate whether there was a statistically significant difference in the test performance of students with disabilities on tests with three response options and tests with four response options. Each of the null hypotheses was rejected at the 95% confidence level based on z-test statistics and probability values. The findings of this study show that there is a statistically significant difference in the academic performance of students with disabilities on tests with three response options. This study provides data for test developers and teachers that can be used to determine the most effective and appropriate number of response options needed to assess the academic performance of students with disabilities. [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.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]