Low confidence toward mathematics is one of the critical issues that diminish students' will to learn mathematics. Several studies indicated that game-based learning (GBL) might be a potential approach to address this issue. In addition, mental calculation, a fundamental mathematical skill, was considered to be a potential skill that may build students' confidence toward mathematics. Thus, this study attempted to promote students' mathematical confidence by incorporating mini-games, a sub-genre of games, into mental calculation learning. A preliminary study was conducted to investigate how students reacted to learn mental calculation in a mini-game environment. The results of the preliminary study suggested that the mini-game-based approach was popular to students. However, it was observed that students' with different levels of academic ability might benefit diversely from the mini-game environment. Thus, an experiment was conducted to investigate how students with different levels of academic ability react to learn mental calculation with mini-games, in terms of two important aspects of learning, i.e., performance and confidence. A control group participated in a paper-based learning approach to provide a baseline of comparison. The results indicated that The mini-games helped both high- and low-ability students gain significant improvement on their mathematical confidence. In addition, the low-ability students learned with mini-games gained more improvement on mental calculation than their paper-based peers did.