In the current technology-driven era, digital game-based learning (DGBL) has emerged as a practical approach for enhancing mathematics achievement among young students. It is believed that digital drill-and-practice educational games can replace traditional pen-and-paper drills in mathematics education and have a better influence on incorporating postgame debriefing activities. The current study applied a quasi-experimental study mixed-method design to evaluate the differences in mathematics learning achievement and learning retention between three types of interventions of PaGamO, PaGamO with postgame group discussions, and pen-and-paper drills among sixth-grade elementary students in mathematics courses. Greater improvements were observed among students learning with PaGamO compared with traditional pen-and-paper drills. Positive perceptions of PaGamO among students were confirmed through semi-structured interviews. However, students who participated in postgame group discussions exhibited impaired learning retention, suggesting that the immediate effects of DGBL with postgame discussions are positive but that the delayed effects are adverse. Implications of the study findings and suggestions for future research are also provided for broader and practical application of PaGamO and postgame activities in educational settings.