ABSTRACT Purpose Early childhood is a crucial time to develop fundamental motor skills (FMS) such as throwing, running and kicking (Goodway, J. D., J. C. Ozmun, and D. L. Gallahue. 2019. Understanding Motor Development: Infants, Children, Adolescents, Adults. Jones & Bartlett Learning.). Existing research into the play-based early childhood curricular in Wales found that children were not making progress in learning object control skills (Wainwright, N., J. Goodway, M. Whitehead, A. Williams, and D. Kirk. 2018. “Laying the Foundations for Physical Literacy in Wales: The Contribution of the Foundation Phase to the Development of Physical Literacy.” Physical Education and Sport Pedagogy 23 (4): 431–444. https://doi.org/10.1080/17408989.2018.1455819.). This was a concern as object control skill competency is critical to physical activity later in childhood and adolescence (Barnett, L. M., E. Van Beurden, P. J. Morgan, L. O. Brooks, and J. R. Beard. 2009. “Childhood Motor Skill Proficiency as a Predictor of Adolescent Physical Activity.” Journal of Adolescent Health 44 (3): 252–259. https://doi.org/10.1016/j.jadohealth.2008.07.004.). Therefore, SKIP (Successful Kinaesthetic Instruction for Pre-schoolers) – Cymru (Welsh word for Wales), a programme of professional development was developed based on the evidence-based work of SKIP by Goodway and colleagues (Goodway, J. D., J. C. Ozmun, and D. L. Gallahue. 2019. Understanding Motor Development: Infants, Children, Adolescents, Adults. Jones & Bartlett Learning.) to address the gaps in teacher knowledge. A limitation of previous SKIP and motor development literature is the lack of evaluation of the teacher’s fidelity to implementation. Ensuring fidelity of implementation (FoI) is a critical indicator of quality intervention programmes. Thus, this study examined the extent to which teachers could implement a 10-week SKIP-Cymru programme with fidelity with ongoing mentoring following a programme of professional development. Method Participants: Early childhood teachers (N = 5), with no prior experience of SKIP Cymru, from 4 Welsh schools took part in the study. Mentors (N = 2) supported the teacher’s implementation of SKIP Cymru following the one-day professional development workshop. Quantitative data were collected using fidelity checklists for both the Teacher Workshop and the implementation of SKIP Cymru. Descriptive statistics of fidelity data were calculated. Results The results for the Teacher Workshop found that 100% of the content was delivered in relation to the Core Instructional Principles, Practices and Expectations of the SKIP-Cymru, and teachers learned the key outcomes. The average teacher fidelity for implementation of SKIP Cymru was 67.80% (ranging between 39% and 89%). On average the teachers delivered 16.4 out of the 20 lessons. The mentors supported the teachers for an average of 7.4 lessons out of the 10 lessons. Conclusion This study demonstrates that it is possible to train teachers to deliver a developmentally appropriate motor skills programme. Nevertheless, it was evident from the inconsistencies in implementation that teachers needed more in-depth knowledge, and specifically a lot more time to develop the pedagogical and instructional skills needed to optimize the impacts of SKIP Cymru on children. It is recommended that the current model of professional development needs to be re-evaluated, with consideration being given to either more in-depth training for mentors or more in-depth accredited training for the teachers that would negate the need for mentoring and have a bigger impact on the teacher’s pedagogy and delivery.