Research on school-based prevention suggests that the success of prevention programs depends

on whether they are implemented as intended. In antibullying program evaluations, however,

limited attention has been paid to implementation fidelity. The present study fills in this gap by

examining the link between the implementation of the KiVa antibullying program and outcome.

With a large sample of 7413 students (7–12 years) from 417 classrooms within 76 elementary

schools, we tested whether the degree of implementation of the student lessons in the KiVa

curriculum was related to the effectiveness of the program in reducing bullying problems in

classrooms. Results of multilevel structural equation modeling revealed that after nine months

of implementation, lesson adherence as well as lesson preparation time (but not duration of

lessons) were associated with reductions in victimization at the classroom level. No statistically

significant effects, however, were found for classroom-level bullying. The different outcomes for

victimization and bullying as well as the importance of documenting program fidelity are

discussed.