The present study extends the literature by investigating the relative salience of self- and collective efficacy in predicting group performance among early adolescents in Indonesia. A total of 435 early adolescents (mean age 11.70 years, 53% female) were randomly assigned to groups of three to four and completed three group tasks (task 1: puzzles; task 2: math; task 3: puzzles). Results indicated that collective efficacy was a more salient predictor of group performance than self-efficacy. Examination of the interaction effects suggested that the positive effects of collective efficacy on task performance were moderated by the levels of individual members' self-efficacy, that is, when group members' self-efficacy was high, task performance was lower. However, the debilitating effect disappears in the last task, where self-efficacy no longer undermines task performance when group members' collective efficacy is high. Interestingly, heterogeneity of the group in terms of gender and ethnicity composition significantly predicted task performance of the group: groups comprising more boys and groups comprising members of different ethnic backgrounds had lower task performance. Findings are discussed in relation to their theoretical contributions and applied implications for classroom teaching and learning.