This study examined the association between two implementation factors, nurse-reported intervention adherence and self-efficacy, and children's outcomes in school nurse-delivered anxiety interventions. Data were collected in a pilot randomized controlled effectiveness trial with 54 children and 21 school nurses. Nurses implemented either a cognitive behavioral or relaxation-skills-only intervention. Nurse questionnaires assessed implementation factors. Independent evaluators assessed changes in children's anxiety symptoms at postintervention and at 3-month follow-up using clinical improvement and global functioning scales. Regression analyses indicated that greater intervention adherence was associated with greater anxiety symptom improvement at follow-up. Nurse self-efficacy interacted with intervention group, such that nurses with higher self-efficacy who implemented the cognitive behavioral intervention tended to have children show improvement and higher postintervention functioning. The impact of implementation factors on children's outcomes may differ depending on intervention type. Self-efficacy may be important for nurses using relatively complex interventions. Intervention adherence should be supported through training and consultation. [For the corresponding grantee submission, see ED608556.]