Vocabulary is the foundation for students who learn a foreign language. Nevertheless, students may be bored by the painstaking process of rote learning. To this end, this study designed a handheld sensor-based vocabulary game based on a scaffolding strategy for improving students' motivation and achievement in vocabulary learning. On the one hand, such mobile technologies not only help students learn vocabulary anytime and anywhere, but also create embodied learning experiences by allowing students to control the avatar in the game with their hands. On the other hand, the scaffolding strategy adopted in this study serves as a complementary mechanism to help students learn vocabulary. To evaluate the effectiveness of the game, this study conducted a quasi-experiment by dividing the participating students into an experimental group and a control group. The former played the handheld sensor-based vocabulary game based on the scaffolding strategy, while the latter played the same game without the assistance of the scaffolding strategy. The research findings of this study showed that the handheld sensor-based vocabulary game significantly improved the low-achieving students' motivation and performance in vocabulary learning, but seemed to be less effective in helping them retain the vocabulary they learned through the game.