there to see his dream being achieved. My deep gratitude to my sister, Nawal, and to my wife, Batool, for supporting me during a difficult time. Words cannot describe how grateful I am to my advisor, Dr. Youjia Hua. He has been a great inspiration to me on how to become a leading researcher and professor. Throughout my academic years here at the University of Iowa, he has been a caring professor, adviser, and friend. He helped me acquire and expand my knowledge about scientific research, specifically about single case research. He also gave me plenty of opportunities to demonstrate and improve my professional competence by having me work as a teaching and research assistant. Moreover, there were moments where I felt frustrated, stressed out, and overwhelmed, but he was always there to support me in completing my Ph.D. What more could a student ask of an advisor? Words are also insufficient to express my sincere thanks to my thesis committee. I am deeply grateful to Dr. Susanne Woods-Groves for being generous in sharing her rich and thorough knowledge about autism spectrum disorder and assessment and for helping me hone my research skills by having me work with her on some research. I am also very grateful to Dr. Catherine Welch for broadening my knowledge about educational measurement and evaluation and for encouraging my interest in applying measurement concepts to assessing students with disabilities. I would also like to express my sincere gratitude to Dr. Allison Bruhn and to Dr. Shawn Datchuk for their helpful advice on my dissertation. v I would like to say a sincere thank you to Josephine Fernando and Saeed Alqahtani for their support and help throughout my Ph.D. and to Jing Zhu for her valuable suggestions about my dissertation. I am also grateful to Mubarak Aldawsari for helping me recruit the participants and implement the interventions. Finally, this work would not have been done without the enduring support of my best friend Ibrahim Alkhodairy who has my profound, undying gratitude; I cannot thank him enough for everything he has done for me. vi