||A plethora of research exists regarding various teaching techniques and interventions for autism. By consolidating and analyzing the available research, effective interventions may be identified which can help lead to better practices. Parents, teachers, clinicians, and care providers, in addition to individuals with autism, stand to benefit from a systematic evaluation of the treatment modalities available for increasing functional communication skills in children with autism. A statistical analysis was performed on the available data using the computer program, Hierarchical Linear Modeling (HLM), which allowed for analyses of participants nested within studies. Effect sizes (ES) were calculated for PECS, Sign Only Communication and Total Communication interventions described in the research. This common metric allowed for comparisons to be made between treatments while taking individual differences into account. This meta-analysis included 43 single-subject outcome studies completed between 1965 and 2004. Quantitative results indicated that total communication (TC) interventions resulted in the largest mean effect sizes. Additionally, several participant characteristics (e.g., adaptive score, age, IQ, receptive language score, verbal/nonverbal classification) and one study characteristic (e.g., data base) were found to moderate treatment effectiveness. The practical implications from these results are vast. First and foremost, regardless of personal preference, it is critical that practitioners understand that TC interventions always resulted in the greatest treatment gains, making it difficult to suppose a situation that either SIGN or PECS be implemented over TC. Second, even though individuals with autism can be difficult to accurately assess using standardized measures, it is critical that practitioners and researchers attempt to get accurate pretreatment scores being that many are highly predictive of individual outcomes. Finally, the results help lay a foundation for future research aimed at comparing topography-based and selection-based communication interventions.