The purpose of this study was to investigate the effects of explicit Direct Instruction to teach letter sound correspondence to students with developmental disabilities. Additionally, this study sought to provide a basis for further research for a population of students with low incidence disabilities who are oftentimes overlooked in the field of education. The intervention included identification of letter sound correspondence using verbal and nonverbal methods of response; thus, providing opportunities for students with severe communication disorders to demonstrate skill knowledge. Picture probes measured student's ability to transfer skill knowledge of letter sounds to another format. All participants reached mastery. Visual analysis revealed a functional relation between explicit Direct Instruction and the percentage of correct responses on letter sound correspondence probes. The intervention achieved social validity as evidenced by positive feedback received on validity questionnaires. Implications for the intervention and the need for future research with similar populations of students with disabilities 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.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]