In this research, the effects of cooperative learning on mathematics achievement in Turkey were examined by meta-analysis method. For this purpose, the average effect size value and the average effect size values of the moderator variables (cooperative learning technique, education level, learning domain and implementation period) were calculated. MetaWin and Comprehensive Meta-Analysis (CMA) statistical programs were used for the analysis. Based on the inclusion criteria, 59 effect size values for 47 studies were calculated. Hedges's g coefficient was used when the effect sizes were calculated and the confidence level was accepted as 95%. The average effect size value was 0,840 with 0,077 standard error which was calculated by the random-effects model. As a result, the effects of cooperative learning on mathematics achievement is moderate and positive.