This study utilized data from the evaluation of the Finnish KiVa program in testing the prediction that school bullies' high perceived popularity would impede the success of anti-bullying interventions. Multiple-group structural equation modeling (SEM) analyses were conducted on a subsample of 911 third-, fourth-, and fifth-graders identified as perpetrators of bullying. They belonged to 77 Finnish schools, including 39 schools implementing the KiVa program and 38 control schools. Data on peer-reported bullying and perceived popularity were collected before program implementation and one year later. Controlling for sex, age, and initial levels of bullying, KiVa participation resulted in lower rates of bullying (indicated by fewer peer nominations) after one year for bullies of low and medium popularity. However, there was no significant effect for those high in popularity, suggesting that popular bullies are less responsive to anti-bullying interventions than less popular bullies.