Background: The involvement of school-age children in participatory research is described in the context of a school district-university partnership to prevent obesity in children. The purpose of this study was to elicit, from children in kindergarten (K) through sixth grade, perceptions of foods and activities that would inform the design of developmentally appropriate interventions to prevent and reduce childhood obesity. Methods: Children (N = 218) were selected through a random sample of K through sixth grade classrooms in 3 schools. They participated in structured, interactive, small group exercises focused on perceptions of foods (taste and healthy/unhealthy) and activities (fun and active/sedentary). High school students in the same school district were trained to facilitate the children's groups in collaboration with university faculty and students. Results: Qualitative data analysis was used to discern patterns across grade levels. There were grade-level differences in perceptions of the taste and healthfulness of foods. Younger children (K-1) equated foods that tasted good with foods that were "good for you." Older children were more discriminating and gave reasons for their perceptions. For activities, fun was positively associated with the number of people involved and the amount of movement. There were fewer differences across grade levels in preferences for types of sedentary activities, compared with sports and other activities that "make you move." Conclusions: The findings have implications for developmentally appropriate health promotion interventions to prevent obesity. These structured but highly interactive methods could be used by school personnel to assess the unique needs of a school population. (Contains 2 tables and 2 figures.)