This study was carried out during an intervention program tackling bullying in classrooms. The study's main aim was the exploration of emotional expressions (verbal and nonverbal) of bullies, victims and bystanders, the hypothesis being that these children react in emotionally different ways. The intervention program was carried out in an Italian elementary school over a period of 8 months. The sample of the study included 6 experimental classes (in which intervention strategies were carried out) and 3 control classes (in which the normal curriculum was used). Peer nominations were used to single out bully, victim and bystander children. In experimental classes Cooperative Group Work (CGW) was carried out once a week. This was video-recorded and so was children's behaviour in the playground. Using these videos children were interviewed at the beginning and at the end of the intervention by means of Interpersonal Process Recall (IPR, Kagan and Kagan, 1991). These interviews were also video-recorded, and then analysed using content analysis for the verbal emotional expressions and the Maximally Discriminative Facial Movement Coding System (MAX, Izard, 1979) for facial expressions. Moreover, naturalistic observation in the playground was carried out using a behavioural check list, again at the beginning and at the end of the intervention. Results show that during IPR victims displayed significantly less verbal and non verbal emotional expressions than bullies and bystanders, and that the latter showed indifference towards victims' experience. In the last interview more empathy and more awareness about their own and the others' emotions was found in most children. Some bullies and some victims did not show any change in the considered behaviours. Both victims and bystanders showed improvement of social skills during playground activities. Finally, peer nomination scores of bullies and victims of experimental classes significantly improved compared to those of control classes.