Despite the growing interest in digital game-based learning (DGBL), there has been a lack of attention paid to the effects of individual differences, such as gaming flow experience and gender differences, in a reward-based achievement system. To this end, this study developed an achievement system with a reward mechanism to facilitate English learning. This study investigated how individuals' gaming flow experience levels affected their levels of learning motivation, and whether any gender differences existed in gaming flow experience and learning motivation while engaging in the achievement system. The results showed that gaming flow experience significantly predicted learning motivation, whereby the students with high gaming flow experience were six times more likely to have high learning motivation than those with low gaming flow experience. Subsequent analysis showed that the female students had significantly higher gaming flow than the male students, but the male and female students showed similar learning motivation. Furthermore, the results indicated that the male students achieved more interactive rewards than the female students, but no significant differences were found in the male and female students' achievement of other types of rewards. Based on these findings, the authors contribute to the literature by developing a framework which can be applied to support designers to accommodate individual differences in DGBL.