To investigate the effect of psychosocial interventions on emotion regulation outcomes in children and youth (0-23 years). We conducted a meta-analysis using a three-level modeling approach extracting multiple effect-sizes from experimental and quasi-experimental studies. We included 40 interventions from 35 publications involving 3,891 participants and extracted 258 posttreatment effect sizes. Analyses were performed to assess intervention effects on emotion regulation, moderating effects of inclusion of acceptance focus and other potential moderators. Additionally, we examined intervention effects on mental health outcomes. Interventions showed a significant small-to-medium effect on emotion regulation (d = 0.37, 95% CI [0.22, 0.51], p < 0.001). Similar effects on were found regardless of acceptance-focus. Interventions significantly associated with a higher level of effect (p [less than or equal to] 0.045) included ACT, DBT, CBT and behavior parent training interventions. Significant small-to-medium effects were found for mental health outcomes (d = 0.39, 95% CI [0.25, 0.53], p < 0.001), with a correlation of 0.56 between overall outcomes across domains. Meta-regression results indicated that psychosocial interventions are moderately effective in improving emotion regulation, with no significant difference in inclusion of acceptance-focus. Findings suggest that emotion regulation is a transdiagnostic process that may inform the development of more beneficial interventions.