Meta-analyses on the effect of peer tutoring have rarely examined the effect of peer tutoring on tutors' academic gain. Some previous analyses are dated and have methodological or theoretical limitations. Hence, there is a compelling need to fill this gap by conducting an updated and comprehensive meta-analysis for identifying certain determinants of best practices for peer tutoring on tutors' academic achievement in the present study. Additionally, role theory and equity theory in peer tutoring were tested. The present meta-analytic study examined 16 articles using The comprehensive meta-analysis software programme and SPSS macro for analyses. It was found that the weighted mean effect size was 0.43 (p < 0.001). Moreover, the crucial parameters for optimizing the effectiveness of peer tutoring interventions are identified as follows: Tutees with low academic ability; tutors coming from secondary school; fewer tutor training sessions per week; shorter tutor training time per session; choosing mathematics as subject content; random assignment of tutees and tutors; structured peer tutoring; same-age non-reciprocal peer tutoring; same-sex dyad grouping; and more weekly tutoring sessions but longer tutoring time for each session.