Adolescent obesity is an increasing challenge, and pervasive social health games hold much promise for promoting sustained healthy behaviors. Researchers and designers of these systems have many potential theories and existing best practices at their disposal. Our study, grounded in participatory design, shows which ones matter—both for pervasive social health games and within the cultural context of a community we studied over the course of three years. We worked with 112 US middle school students from a lower-income community in a series of participatory design exercises focused on social rewards for everyday physical activity. In our analysis, we discuss design implications in four key areas: social presence, gender effects, incentives and competition. We show how these themes manifested in students’ designs and why they were particularly important to our participants. We then use our findings to suggest design strategies for youth-focused pervasive social health games.