This paper describes the deployment of a novel ubiquitous behaviour change system for social interaction and reflection amongst school children. For four weeks, a class of schoolchildren (Year 5) was monitored with Fitbit activity monitors and their daily physical activity was visualised on a custom ambient display. In addition, video segments describing mission-based activities were shown on tablet devices to the children at the start of each week. The ambient display would indicate if they performed better than the previous day. We describe how the system was designed and developed, present findings from the in-the-wild study, and provide design guidelines for future studies.