Numerous interventions to address posttraumatic stress (PTS) in youth exposed to mass trauma have been delivered and evaluated. It remains unclear, however, which interventions work for whom and under what conditions. This report describes a meta-analysis of the effect of youth mass-trauma interventions on PTS to determine if interventions were superior to inactive controls and describes a moderator analysis to examine whether the type of event, population characteristics, or income level of the country where the intervention was delivered may have affected the observed effect sizes. A comprehensive literature search identified randomized controlled trials (RCTs) of youth mass-trauma interventions relative to inactive controls. The search identified 2,232 references, of which 25 RCTs examining 27 trials (N = 4,662 participants) were included in this meta-analysis. Intervention effects were computed as Hedge’s g estimates and combined using a random effects model. Moderator analyses were conducted to explain the observed heterogeneity among effect sizes using the following independent variables: disaster type (political violence versus natural disaster); sample type (targeted versus non-targeted); and income level of the country where the intervention was delivered (high- versus middle- versus low-income). The correlation between the estimates of the intervention effects on PTS and on functional impairment was estimated. The overall treatment effect size was converted into a number needed to treat (NNT) for a practical interpretation. The overall intervention effect was statistically significant (g = 0.57; P < .0001), indicating that interventions had a medium beneficial effect on PTS. None of the hypothesized moderators explained the heterogeneity among the intervention effects. Estimates of the intervention effects on PTS and on functional impairment were positively correlated (Spearman’s r = 0.90; P < .0001), indicating a concomitant improvement in both outcomes. These findings confirm that interventions can alleviate PTS and enhance functioning in children exposed to mass trauma. This study extends prior research by demonstrating improvement in PTS with interventions delivered to targeted and non-targeted populations, regardless of the country income level. Intervention populations and available resources should be considered when interpreting the results of intervention studies to inform recommendations for practice.