© 2019 Human Kinetics, Inc. This study examined the effectiveness of a physical activity (Year 1) and a multicomponent fundamental movement skill (FMS) (Year 2) intervention on primary school children's FMS proficiency. Data were collected from 6- and 10-year-old cohorts from two intervention schools and age-matched groups from one control school, in south Ireland. In Year 1 (N = 187), intervention (n = 96) and control (n = 91) groups were children from senior infant (6-year-old cohort) and 4th class (10-year-old cohort). In Year 2 (N = 357), intervention (n = 195) and control (n = 162) groups were children from senior infant and 1st class (6-year-old cohort) and 4th and 5th classes (10-year-old cohort). FMS assessment was conducted across both academic years, using the Test of Gross Motor Development-2. Linear mixed models were used to investigate the effectiveness of each intervention, adjusting for age group. Following Year 1, the intervention group significantly improved locomotor proficiency (p <.05), with no changes in object-control or overall proficiency. No group-time interactions were found. Following Year 2, the intervention group significantly improved locomotor, object-control, and overall proficiency (p <.001). Group-time interaction effects were found for both subsets and overall FMS in favor of the intervention group (p <.001). FMS proficiency among primary school children was significantly greater following the multicomponent FMS intervention.