The ViSC program is the first evidence based anti-bullying program implemented in Turkey. A quasi-experimental longitudinal control group design comprising six schools and 26 classes was realized to examine the program effectiveness regarding different forms of perpetration and victimization. The effectiveness of two dosages of interventions--school and class level vs. school level--was investigated. In total, 642 grade 5 students (227 in school and class level, 201 in school level, 214 in control group, 49% girls, M[subscript age]?=?10.06) participated. Multilevel growth models revealed baseline effects indicating that the two intervention groups had lower levels of perpetration and victimization at pre-test than the controls. Perpetration and victimization increased in the two intervention groups compared to control group between pre- and post-test, but also decreased between post-test and follow-up indicating a sensitizing effect of the program. Results are important for both intervention research and social policy in Turkey.