This study aimed to examine the effect of using the flipped classroom model on students' proportional reasoning. In this context, the study focused on students' achievement and solution strategies for proportional reasoning problems. The participants of the study were 56 seventh-grade students, who were determined by convenience sampling method. In line with the purpose of the research, the concept of proportion was taught to the experimental group using the flipped classroom model and to the control group through teaching in accordance with the mathematics curriculum. The data of the study were collected through the Proportional Reasoning Test. The results of the study showed that the flipped classroom model was more effective in terms of mathematics achievement than the teaching method in line with the curriculum. In addition, the experimental group students used more correct solution strategies and fewer incorrect solution strategies than the control group students while solving the problems.