Objectives. We investigated whether intervention effects of FRIENDS for Life, a school-based prevention program for children with anxiety or depression symptoms, were maintained over a period of 12 months after the intervention in a naturalistic setting. Methods. We used a quasi-experimental design, with 339 children in the intervention group and 157 in the control group (aged 8?13 years) in schools in Amsterdam, the Netherlands. We collected self-, teacher, and peer reports of anxiety and depression scores before and after intervention, and 6 and 12 months after intervention, from 2010 to 2012. Results. Intervention-group children reported a continuing and significant decrease in anxiety and depression scores compared with the control group. Twelve months after the intervention, participants' anxiety and depression levels were comparable to those of the general population. Girls reported a stronger decrease in anxiety scores than did boys. Teacher reports suggested no effects. Although classmates reported increased internalizing problems in intervention-group children immediately after intervention, these effects disappeared over time. Conclusions. FRIENDS for Life, an indicated prevention program, yielded long-lasting and continuing reduction in anxiety and depression problems when implemented in daily school practice.