Purpose: Competence in fundamental movement skills (FMS) is purported to be linked with increased physical activity participation. Yet, recent research suggests a low level of FMS proficiency in children. The aim of this study was to evaluate the efficacy, impact on gender, and influence of teacher fidelity on the Moving Well-Being Well intervention. Method: The intervention was delivered in 18 primary schools (n = 925, M[subscript age] = 7.55 years). Data were gathered on six FMS and two balance skills pre- and postintervention using the Test of Gross Motor Development--Third Edition and Bruininks--Oseretsky Test of Motor Proficiency 2. Results: The mean postintervention FMS score was higher than preintervention, with a mean increase of 7.85 (23%). A two-way analysis of covariance found gender was not statistically significant (p = 0.74), but teacher fidelity was statistically significant (p = 0.000; moderate effect size). Conclusions: The intervention significantly improved children's FMS, having a similar effect on boys and girls. Teacher fidelity of implementation had a significant impact on FMS improvement.