Location Based Games (LBGs) can support various learning activities in both formal and informal settings. Furthermore, the fact that they can utilize players' physical movement for players' advancement in the game world makes them an appealing alternative for promoting physical activity in students. However, LBGs are not sufficiently used in education with one reason being that their development requires advanced technical skills that school teachers often lack. The aim of this study was twofold: (a) the design and development of an open-source platform for the simplified creation of multi-player educational LBGs that require players' physical activity, by persons that possess basic computer or smartphone use skills, such as school teachers, and (b) the evaluation of the platform, and specifically of its game design environment, by school teachers as to its perceived usability and acceptance. YOUth Go comprises a Game Designer Environment (GDE), that the designer uses on any device to create a game, and a Game Player Environment (GPE), that the player uses on a GPS enabled Android or iOS device to play the game outdoors. Eighty-four (84) randomly selected in-service teachers attended a three-hour online seminar on mobile learning, LBGs and the use of the GDE. During it, they started creating their own games, that they could complete in their free time for two weeks, after which, they answered an online questionnaire on the usability and acceptance of the GDE. The usability of the GDE was perceived to be good by the teachers, who found it to be user-friendly and did not encounter particular difficulties with it. They were highly satisfied from the GDE, which they perceived as a useful tool for their work, did not feel anxiety about, but had very positive attitudes towards using it, with their intention to use it in the future being high. The findings suggest that teachers are likely to adopt YOUth Go as a tool for promoting students' learning and physical activity.