The Picture Exchange Communication System (PECS) is an augmentative and alternative system (AAC) used to improve and increase communication for children with Autism Spectrum Disorder (ASD) and other developmental disorders. Research addressing the efficacy of this system is increasing; however, there is limited information published that evaluates the picture type used for PECS instruction. A single-subject alternating treatments design was used to examine the role of iconicity, or how closely a symbol resembles its referent, in the acquisition of picture discrimination in the third phase of PECS. The purpose of this study was to compare how well children were able to discriminate pictures with high iconicity versus pictures of low iconicity in Phase 3 of PECS. Four preschool children from 22-36 months of age with ASD or an Early Childhood Developmental Delay participated in the study. The results indicate that that there was minimal difference in picture discrimination between the two picture types. Children learn to discriminate equally well with pictures of low or high iconicity in the third phase of PECS instruction. [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.]