Previous research has demonstrated the relationship between high cohesion and optimal team performance. This study investigated the cohesion-individual performance relationship and examined expended effort as a mediator of that relationship. At the middle and end of the regular season, 41 male and 49 female varsity high school basketball players representing eight teams completed measures of group cohesion and perceived expended effort. At the same time intervals, the players’ game statistics were gathered, and coaches completed the expended effort questions regarding their players. Results partially supported the predictive ability of cohesion on objective individual performance and expended effort was a mediator of the cohesion-individual performance relationship at the end of the season. Results are discussed regarding theoretical and measurement issues. Practical implications for coaches and consultants are also provided.