A meta-analytic study on effectiveness of behavioral and psychotherapeutic treatments for challenging behaviors in individuals with mild mental retardation is reported. Eighty articles were examined. For each comparison, several study variables and two effect sizes (percentage of nonoverlapping data—PND and percentage of zero data—PZD) were evaluated (Ms = 75% and 35%, respectively). Studies in which experimental designs and methods of experimental functional analysis were used had significantly larger PNDs than those with AB designs and descriptive methods, respectively. Functional analysis, reliability of recording, generalization, and internally valid designs resulted in larger PZDs. We found that behavioral interventions for challenging behaviors are effective with people with mild mental retardation.