This short-term longitudinal study examined whether individual moral disengagement and classroom collective moral disengagement were associated with offline and online bullying over the course of 1 year. Multilevel growth modeling with three levels was used to analyze data from a sample of 1048 Swedish students in 68 classrooms. The students completed a self-report questionnaire at two time-points separated by approximately 1 year. All students were in fifth grade (M_age = 11.5) at the first timepoint and in sixth grade (M_age = 12.6) at the second timepoint. Results showed that students reported more offline and online bullying if they had higher initial levels of individual moral disengagement and if they belonged to classrooms with higher initial levels of classroom collective moral disengagement. Also, a change in individual moral disengagement was positively associated with a change in bullying others offline and online.