Achalasia, a rare esophageal motility disorder characterized by the inability of the lower esophageal sphincter to relax and loss of esophageal peristalsis, significantly impacts pediatric patient quality of life through symptoms like dysphagia, chest pain, and weight loss. This nationwide retrospective cohort study evaluates the efficacy and safety of peroral endoscopic myotomy (POEM) for pediatric achalasia in Mongolia, contributing to the limited global data on this minimally invasive treatment in children. Conducted between February 2020 and March 2022 at 2 tertiary centers, the study included symptomatic achalasia patients, treatment-naive or those with unsatisfactory outcomes from previous esophageal dilations. The POEM procedure was assessed for its impact on esophageal structure and function, symptom severity via the Eckardt score, and procedure-related safety, with outcomes measured at baseline, 3 days, and 12 months post-procedure. The study demonstrated notable post-procedure improvements across all measured outcomes: abnormal contraction length and esophageal width significantly reduced, underscoring the procedure's effectiveness. More precisely, the integrated relaxation pressure showed a significant improvement from a mean of 26.8 mm Hg (standard deviation [SD], 5.4 mm Hg) pre-procedure to 10.8 mm Hg (SD, 1.1 mm Hg) 12 months (P < .001). Similarly, Eckardt scores, which assess symptom severity, improved significantly from a pre-procedure mean of 7.0 (SD, 1.0) to a substantially lower score post-procedure (P < .001), reflecting enhanced patient quality of life and symptom alleviation. This study underscores POEM's role as an effective, minimally invasive option for pediatric achalasia management within the Mongolian population, offering significant symptomatic relief and improved esophageal function.