An experiment was conducted with 30 groups (n = 120) solving brainstorming tasks under four different group goal conditions: do your best (DYB), directive group goal setting (DGGS), participative group goal setting (PGGS), and PGGS in combination with individual goal setting (PGGS + IGS). As expected, all groups with specific and difficult group goals performed better than DYB control groups. It is hypothesized that these positive effects of group goal setting on brainstorming performance arise because group goal setting counteracts motivation losses such as social loafing. In addition, group goal setting should promote motivation gains arising from social compensation and related cognitive processes, in particular high identification with the group. Consistent with this hypothesis, it was found that group goal setting increased team identification, the readiness to compensate for other weak group members, the value of group success, and the value of group failure. Mediation analysis also indicated that concern to avoid group failure was partly responsible for performance improvements. Finally, no large differences were found between PGGS + IGS and PGGS or DGGS. On this basis group goal setting can be considered a robust strategy for improving work motivation and brainstorming performance in groups.