Chronic non-cancer pain in children and adolescents can be impairing and results in substantial health care costs. Intensive Interdisciplinary Pain Treatment (IIPT), an inpatient or day hospital treatment delivered by a team of three or more health professionals, may be an effective intervention for these children and adolescents. Based on previous reviews and meta-analyses, we updated the findings regarding the description of available treatments and estimated the effectiveness of IIPT, overcoming methodological shortcomings of previous work by requesting and analyzing individual participant data. On June 26, 2021, we searched five literature databases (PubMed, PsycINFO, Web of Science, Cochrane Library, and PubPsych) for studies examining the effectiveness of IIPT. Included studies employed a pre-post design, assessed patients under the age of 22 years, and presented their results in English, German, French, or Spanish. We used standard methodological procedures expected by Cochrane to pool treatment effects and assess risk of bias. We identified 13 different treatment sites with similar treatment inclusion criteria and treatment components, but the descriptions of those treatments varied widely. Regarding treatment effectiveness, IIPT may result in large improvements in mean pain intensity (g=-1.28), disability (g=-1.91), and number of missed school days at 12-month follow-up (g=-0.99), as well as moderate improvements in anxiety (g=-0.77) and depression (g=-0.76). The certainty of the evidence, however, was graded very low to low. We recommend future researchers employ more scientific rigor to increase the certainty of the evidence for IIPT and to standardize treatment outcomes for children and adolescents with chronic pain.