Introduction: Recent evidence suggests that young people are insufficiently active to benefit their current and future health, and of particular note is the age related decline occurring during adolescence. Underpinning the necessity of an active lifestyle, fundamental movement skills (FMS) are deemed the building blocks for movement. Most recently, the World Health Organisation (WHO) identified the need for school-based policy interventions to increase physical activity (PA). Purpose: The purpose of this research was the design, development, implementation and evaluation of a targeted whole school PA intervention (Y-PATH: Youth-Physical Activity Towards Health) for early adolescent youth (12 to 14 years) in Irish post-primary schools. Methods: Information was gathered on participants (n = 256) levels of PA, BMI, and FMS proficiency. A sub sample of participants (n = 59) also participated in focus group interviews to explore their perceptions of health. Based on this data, and an exploration of the literature, the Y- P A TH intervention was developed. A quasi-experimental, non-randomised controlled trial involving two schools was implemented to evaluate the Y -P A TH intervention efficacy. Participants’ data (n=174) was collected at 3 time points (pre, post and retention) on the following variables; PA levels, FMS proficiency and BMI. Results: Both schools showed significant increases in daily PA and FMS proficiency over the three time periods. A repeated measures ANOVA showed a significant interaction effect between school attended and time for PA (F(2, 38)= 6.177, p=0.005) and FMS (F(2, 100)=4.132, p=0.019), with a significantly greater increase in PA and FMS observed in the intervention school. Conclusion: Preliminary findings provide support for the simultaneous focus on health related activity (HRA) and FMS in school PE class, along with parent and teacher involvement, in efforts to improve PA levels of adolescent youth. Further research involving a randomised trial with a larger sample size is warranted.