Background: Multi-component psychological interventions may mitigate overweight and obesity in children and adolescents. Evidence is, however, scattered on the effectiveness of such interventions. This study aims to review the available evidence on the effectiveness of multi-component psychological interventions on anthropometric measures of school-aged children with overweight or obesity. Methods: We systematically searched international databases/search engines including PubMed and NLM Gateway (for MEDLINE), Web of Science, SCOPUS, and Google Scholar up to November 2022 for relevant articles pertaining to psychological weight-loss interventions targeting school-aged children. Two reviewers screened and extracted pertinent data. The quality of included studies was assessed using the Cochrane Risk of Bias Tool for Randomized Trials. Random effect meta-analysis was used to calculate, and pool standardized mean differences (SMD). We distinguished between intervention and maintenance effects. Intervention effects were defined as the mean change in outcome measurement detected between baseline and post-treatment. Maintenance effects were defined as the mean change in outcome measurement between post-treatment and last follow-up. Results: Of 3,196 studies initially identified, 54 and 30 studies were included in the qualitative and quantitative syntheses, respectively. Most studies reported on group-based interventions. The significant effects of intervention on BMI z-score (SMD -0.66, 95% CI: -1.15, -0.17) and WC (SMD -0.53, 95% CI: -1.03, -0.04) were observed for interventions that centered on motivational interviewing and cognitive behavioral therapy, respectively. Mean BMI and WC did not differ significantly between post-treatment and last follow-up measurement (maintenance effect), indicating that an initial weight loss obtained through the intervention period could be maintained over time. Conclusions: Findings indicate that motivational interviewing and cognitive behavioral therapy as interventions to reduce BMI z-score (generalized obesity) and waist circumference (abdominal obesity) are effective and durable. However, detailed analyses on individual components of the interventions are recommended in future effectiveness studies.