A sample of 94 children who attended third, fifth, and sixth grade classrooms was used in order to explore children's emotional reactions when their (same-sex) partner in a cooperative computer game appeared to be unable or unwilling to do his or her share in the joint endeavor. During the ensuing discussions dominance in the shape of disgust or contempt made up 18 % of all facial expressions. Different types of smiles, however, were far more frequent - they made up almost half of all facial expressions. Hierarchical regression analyses which were guided by a theoretical model suggest that children showed more often expressions of anger and denigration on their faces when they considered themselves to be rejected by their peers, when their relation ship with their play partner was overshadowed by competition (girls only), and when they experienced intense anger and contempt at the same time. Implications of dominance and denigration for the partner and the cooperation as well as the need of furthering the development of emotional competence are discussed.