Abstract
Finding ways to support children in meeting suggested physical activity levels is a worldwide challenge. Current article introduces the design and development process of the Estonian nationwide comprehensive physical activity program Schools in Motion (SiM) which aims to increase the physical activity levels of children in school settings where schools are active partners in the development and implementation process. The SiM program began with 10 pilot schools in 2016 and has now reached 110 schools in 4 years, with yet more schools eager to join. The program is very popular among schools and has received a positive reception among the governors and society at large. The article describes and analyses the key elements of the planning, piloting, implementation, and scaling phases of the SiM program to give a deeper understanding of the development and the design process of nationwide physical activity intervention programs. In addition to the process and program description, we have also tried to address the difficulties faced during the development process, the strengths and challenges associated with an interdisciplinary approach, and involvement of schools as experts. The article includes an overview of the lessons learnt and the main focuses of the coming years. We hope this article and our experiences will provide valuable information to practitioners and researchers in the field.