This study investigates the effect of using a realistic situation with modeling characteristics in creating and resolving a cognitive conflict to promote understanding of a changing reference in fraction calculations. The study was conducted among 96 seventh graders divided into 2 experimental groups and 1 control group. The experimental groups coped with a realistic modeling situation in which they had to increase, then decrease, the size of a bag of fries. Results indicate conceptual change and better understanding of the changing reference among students in the experimental groups. The article describes their learning process, showing how their analysis of the situation promoted conflict resolution.