This study intends to develop learning interventions to support students in developing their understanding of percentages. The participants were taken from the sixth grade (around 10 years old) of Primary school of American International School of Rotterdam in the Netherlands. There was a student selected as the focus student. The data were collected from test, student interview, and classroom observation during teaching practices. In general, the findings show that the learning interventions which are designed by utilizing the didactical use of bar model support the student in developing understanding of percentages. In dealing with percentage problem, the student are able to utilize doubling and halving strategy, multiplying or dividing both magnitudes with respect to ratio, adding or subtracting known percentages with respect to ratio, and working as ratio table. In terms of the didactical use of bar model, the bar model plays significant role, such as: First, bar model is a powerful model helping student seeing the ratio relationship of the two magnitudes, the percentage magnitude and the magnitude where the percentage refers to. Second, bar model assists student in seeing the part-whole relationship of each magnitude. Third, the bar model triggers student to have a flexible way of thinking and various computation strategies. Fourth, the bar model aids the student to do mental computation. Fifth, the bar model helps in holding the track or the trajectory of the calculation process. Sixth, the bar model helps students to mentally and easily switch their thinking from one perspective, percentage magnitude, to another perspective, for example the minute magnitude. Seventh, the bar allows students to do estimation of value on both the percentage magnitude and the magnitude where the percentage refers to. Moreover, the recent study give evidences of the significant impacts of learning context, type of problems being discussed, and the role of teacher in supporting students in constructing and developing their understanding of a certain concept.