This study examined the effects of using an online flexible educational game on students' attitude towards mathematics as compared to the traditional method of solving mathematical problems. Moreover, the study assessed the learning effectiveness of the game and investigated potential gender differences in the game's effectiveness on changing students' attitude. The participants of the study were 79 students who were randomly assigned to a control and treatment group, as well as four coordinator teachers. The game was configurable and it was used as a supplementary teaching method. The intervention lasted 14 weeks and the data collection was based on quantitative measures and interviews. The results of the analysis indicated that the game approach was effective on improving students' attitude towards mathematics and that it also resulted in better learning outcomes in the treatment group as compared to that of the control group. Furthermore, it was shown that the gender of the students did not influence the positive effect of the game on students' attitude. These results suggest that the incorporation of flexible games into the traditional teaching of mathematics could possibly bring beneficial effects.