There has been little published research literature that has focused on using siblings to teach their non-verbal siblings a manual sign to communicate using the mandmodel procedure. The mand- model procedure is a naturalistic teaching strategy which has been demonstrated to improve communication and social outcomes for children with disabilities. This study investigated sibling tutors teaching their sibling tutees to use the manual sign “more” to request a want or need. The four sibling tutees were between the ages of 25 and 26 months and their sibling tutors were between the ages of 9 and 14 years. A multiple probe design across subjects was used for this study. The mand-model procedure, the independent variable, was used by the sibling tutors to teach the sibling tutees the manual sign “more.” The effectiveness of the use of the manual sign “more” was the independent variable. All four of the sibling tutees were able to successfully learn the manual sign and used the sign across maintenance and generalization phases.

This applied dissertation study was designed to inform and advance knowledge regarding research in the area of the effectiveness of functional communication training (FCT) in reducing challenging behaviors among individuals with autism spectrum disorder (ASD) who were nonverbal, by using a quantitative single subject approach. The researcher specifically focused on determining which modality, Picture Exchange Communication System (PECS) or manual sign language, would be the most effective as a replacement behavior to bring about a reduction in challenging behaviors. Previous researchers in the field of FCT did not address this area, thus leaving a gap in the research. The participants for the study were three children with ASD between the ages of 4 and 6. Prior to the start of the study, multiple assessments were administered to assess the function of challenging behaviors, level of functioning, imitation skills, and preferences. The intervention phases consisted of randomly alternating between a session of PECS and manual sign daily with each session consisting of 10 trials. Baseline data was collected to assess preexisting skill level to mand for items. The intervention trials continued until the participants reached mastery level in either modality. Results demonstrated that only PECS was effective for both the participants who completed the study, and for the participant who mastered both manual signing and PECS, PECS had a quicker acquisition rate. Implications from the findings suggest that FCT is an effective intervention in reducing challenging behaviors, and that PECS might be more effective for quick reductions of challenging behaviors. The study is a valuable addition to the current FCT research as it aligns with and extends findings from previous research.