Collective moral disengagement refers to shared group beliefs that morally justify negative actions. This study reports an initial validation of the newly developed Classroom Collective Moral Disengagement Scale (CCMDS) for adolescents. This self-report instrument assesses the degree to which mechanisms of moral disengagement are shared by students in their class. Data were collected from two samples of 486 and 654 adolescents attending middle and high schools in Italy. Through exploratory and confirmatory factor analyses the unidimensional structure of the scale was established. Multigroup analyses demonstrated configural, metric and scalar invariance of the model across age and gender groups. The final version of the scale consists of 17 items and it has good internal consistency and validity. It is concluded that the scale is a promising measure for research concerning group level morality.