Current concerns about a childhood obesity crisis and children's physical activity levels have combined to justify fitness lessons as a physical education practice in New Zealand primary (elementary) schools. Researchers focused on children's understandings of fitness lessons argue that they construct fitness as a quest for an 'ideal' (skinny or muscular) body. The conflation of fitness with thinness, however, is complex and problematic. In this paper, we draw from research conducted with a class of primary school children in New Zealand. Drawing on the theoretical tools of Foucault and utilizing a visual methods approach, we examine how children experience school fitness lessons and construct notions of fitness, health and body. The children's responses illustrated that obesity discourses and body pedagogies 'collided' in a way that shaped understandings of fitness lessons in ways inextricably connected with the avoidance of being fat. The children assumed that fitness lessons increased fitness and that being fit was demonstrated by a 'correct' corporeal appearance. We argue that body pedagogies inside and outside the school gates shape children's ideas about the body in ways which exclude other understandings of bodies, health, and physical activity.