The “double reduction” policy has shown initial success over the past three years. However, parents and off-campus training institutions continue to influence the policy implementation significantly. Aiming to investigate the correlation between private tutoring and academic performance, as well as identify key moderating variables, this study conducted a meta-analysis on 21 primary studies, encompassing 54 independent samples, 79 effect sizes, and 242,601 participants. The findings revealed a low correlation between private tutoring and the academic performance of students. The impact of private tutoring on academic performance was insignificant after the application of the trim-and-fill method. Among the nine moderating variables analyzed, student gender, educational stage, family socioeconomic status (SES), region, tutoring subject, tutoring duration, and type of tutoring class did not significantly influence the effectiveness of private tutoring. The conclusions clarify the common one-sided perceptions people have about the role of private tutoring, offering new insights for education policymakers, researchers, teachers, parents, and students.