Abstract:As students progressed from primary to secondary school, they are exposed to the constant use of calculators in Mathematics. Due to this reason, some of them are becoming too comfortable and too dependent on calculator even for simple arithmetic. Hence, this study was conducted to promote mental computational skills amongst secondary students by using the Bubble Method. A total of 44 mathematics students from two different schools were selected to be the participants of this study and were involved in intervention lessons using the Bubble Method. Based on the analysis result of pre-test and post-test, administered before and after the intervention respectively, 11 students were selected for further interview. Based on the findings, the effect of the students" performance in calculating percentage has been found to be not statistically significant using the Bubble method, however, all the students who were interviewed agreed that the Bubble Method improved their mental computational skill.