At present, environmental issues are of concern to all countries, especially for developing countries, and education on waste sorting is urgent. However, it remains a challenge to improve students' learning achievement and engagement in environmental education. Researchers have pointed out the potential of digital games for promoting students' learning motivation. In addition, the two-tier testing mechanism has been recognized as an effective tool for correcting students' misconceptions and promoting their in-depth thinking. Therefore, this study proposed a two-tier testing-based digital gaming approach. To verify the effectiveness of the approach, a digital game was developed and a quasi-experiment was conducted. The participants were two classes of fifth graders, with one class as the experimental group using the two-tier test-based digital game and the other class as the control group learning with the conventional digital game. The results showed that the digital game-based learning with two-tier testing model was conducive to students' improved academic performance compared with the conventional digital game-based learning model, especially for students in the low-level group, who were able to make greater progress. In addition, the approach was effective in terms of reducing students' cognitive load and improving their flow experience.