Abstarct: The purpose of this research was to investigate the effect of the Peer Leadership Motivational Climate on Team Cohesion and Team Effectiveness. The research method was descxriptive-correlational and cross-sectional. The statistical population consisted of all adolescent volleyball plaxyer students in Kirkuk province, from whom 200 individuals were selected using the convenience sampling method. The research instruments included three standardized questionnaires for Peer Leadership Motivational Climate, Team Cohesion, and Team Effectiveness. For face and content validity, the opinions of ten experts and professors of Sports Management were utilized, and the reliability of the instruments was confirmed using Cronbach’s Alpha. Structural Equation Modeling (SEM) with a variance-baxsed approach (PLS-SEM) was employed to test the hypotheses. Data analysis was performed using SPSS V23 and Smart-PLS 4 software. The findings revealed that the Peer Leadership Motivational Climate has a significant positive effect on both Team Cohesion and Team Effectiveness. Furthermore, Team Cohesion has a significant direct effect on Team Effectiveness. The mediating role of Team Cohesion in the relationship between Peer Leadership Motivational Climate and Team Effectiveness was also confirmed. These findings emphasize the importance of establishing a supportive and motivational environment at the peer level, as this climate, by strengthening internal bonds and increasing team unity (cohesion), indirectly and substantially enhances overall team effectiveness. Practical development programs for teams should include workshops aimed at enhancing members’ mutual motivational skills and building trust to thereby increase team cohesion and realize its direct impact on improving team effectiveness.