This study used multiple methods to examine group processes (information sharing, morale building, planning, critical evaluation, commitment, monitoring, and cooperation) that mediate the effect of relationship level on group performance. The study uses a 2 by 2 experimental design, crossing relationship (friendship vs. acquaintance) as a between-subjects variable and task type (decision making vs. motor) as a within-subject variable. Fifty-three 3-person groups participated in the study, and data from 4 types of measurement were used to analyze the mediating processes between relationship level and task performance. Friendship groups performed significantly better than acquaintance groups on both decision-making and motor tasks because of a greater degree of group commitment and cooperation. Critical evaluation and task monitoring also significantly increased decision-making performance, whereas positive communication mediated the relationship between friendship and motor task performance.