The primary purpose of this study was to develop and validate a System for Observing the Teaching of Games in Physical Education (SOTG-PE). Primary pilot testing of the SOTG-PE was conducted in a large, selective, all-boys secondary school in the north-west of England. Two hundred and eighty three pupils aged 11-16 volunteered as participants for the pilot testing phase of this study. The SOTG-PE coded 1379 minutes of physical education games lessons across three games categories, including invasion, net/wall and striking and fielding. In addition, the teaching interactions of four full-time teachers of physical education and one pre-service teacher were also coded. The inter-observer and intra-observer mean re-test coefficients suggest that the SOTG-PE is valid for evaluating and recording child activity, lesson context and teacher interactions during various physical education games lessons in the UK. (Contains 1 figure and 3 tables.)