Our aim is to discuss how school mathematical activity is modified when students' everyday situations are brought into the classroom. One illustrative sequence--7th grade classes solving problems that required proportional reasoning--is characterized as a system of interconnected activities within the theoretical perspective of activity theory. We discuss the tensions and contradictions that evolve when a generic school procedure emphasized by the teacher meets the specific procedures applicable to everyday situations proposed by the students. We evaluate the modifications that we perceived in the power relationships and other components of the school activity and the expansion of the meaning of those procedures as positive outcomes of how everyday situations were dealt with in school mathematics.