(1) Background: Idiopathic scoliosis can be defined as a complex three-dimensional deformity of the spine and trunk, which occurs in basically healthy children. Schroth scoliosis-specific exercises have shown good results in reducing idiopathic scoliosis progression. This study aimed to critically evaluate the effect size of Schroth's method through a systematic review and meta-analysis. (2) Methods: Four databases were included in the search: PubMed, Cochrane Library, Web of Science, and Google Scholar. The following keywords were used: Schroth exercise, idiopathic scoliosis, Cobb angle, angle of trunk rotation, and quality of life. Only articles written in English that met the following criteria were included in our study: subjects who had idiopathic scoliosis, the Schroth method was applied, and Cobb angle or angle of trunk rotation or quality of life as outcomes. (3) Results: Ten randomized controlled trials were included in this study. The effect size of the Schroth exercise ranged from almost moderate to large, for the outcomes used: Cobb angle (ES = -0.492, p < 0.005); ATR (ES = -0.471, p = 0.013); QoL (ES = 1.087, p < 0.001). (4) Conclusions: The current meta-analysis indicates that the Schroth method has a positive effect on subjects with idiopathic scoliosis.