Efficacious treatment for anxiety and related somatic pain exist but only 30% of children receive adequate treatment. School nurses frequently treat students with somatic symptoms related to anxiety, but are not trained in specific therapeutic skills. This study examined the fidelity (adherence and competence) with which nurses implemented two evidence-based interventions for youth anxiety. Interventions were developed with a workgroup including members of NASN (National Association of School Nurses), tested via open trial, and refined through an iterative process. Nineteen school nurses were randomly assigned to deliver either a cognitive-behavioral or relaxation-skills-only intervention to 51 elementary school children (meeting criteria for anxiety disorder diagnosis or subthreshold symptoms). Hierarchical regressions revealed children experienced significant reductions in anxiety severity, somatic symptoms, maladaptive thoughts, and avoidant behavior after receiving either intervention. Multi-level modeling yielded nurses were highly adherent and showed fair to good competence to both interventions. Fidelity did not differ between the intervention groups; yet nurses in the cognitive-behavioral intervention group utilized significantly more consultation time with expert psychologists and significantly more time to deliver the intervention to students. Nurse adherence significantly predicted reduced parent-reported anxiety, anxiety severity, somatic symptoms, and global functioning post intervention. Nurse confidence significantly predicted competence across groups.