Despite expansive improvements in both treatments and research, the majority of persons with autism use non-empirically supported interventions. One way to decrease the research-to-practice gap involves increasing the direct applicability of research findings to clinical settings. Effectiveness research achieves this goal by identifying treatments that work and are also feasible and acceptable for implementation in the real-world. The present study applies a four-part effectiveness research model consisting of 1) program evaluation, 2) social validation, 3) identification of moderators, and 4) collaboration with consumers, to the Picture Exchange Communication System (PECS). Although PECS is widely used to teach communication to nonverbal persons with autism, most of the research on this intervention focuses on its outcomes under ideal conditions (i.e., efficacy research). Little is known about PECS outcomes under real-world conditions (i.e., effectiveness research). The present study investigated PECS effectiveness in three phases. In Phase I, home and school observations of children with autism who had been taught PECS were used to gain preliminary information on PECS effectiveness. In Phase II, the researcher used this information to develop surveys for parents and teachers. Surveys assessed children's PECS training and PECS use, adult attitudes towards PECS, and allowed for the identification of moderators of PECS effectiveness. Interviews with consumers were then conducted to fine-tune the surveys. In Phase III, the final surveys were widely distributed to parents (n = 77) and teachers (n = 46). Findings demonstrated that PECS training fidelity did not meet the guidelines outlined in the "PECS Training Manual" (Frost & Bondy, 1994, 2002). Further, many children were not using PECS as it was intended (i.e., as a form of generalized spontaneous communication). Despite these mediocre outcomes, participants still demonstrated generally favorable attitudes towards PECS. Analyses also revealed the role that adult variables (e.g., involvement in PECS programs, social validity) played in moderating children's PECS outcomes. These results have direct implications for improving PECS. Further, the study offers support for an effectiveness research model that can be applied to other areas of autism intervention in an effort to decrease the research-to-practice gap. [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.]