Background:
Many students struggle with algebra variable concept learning. Although comparison and game-challenge are effective strategies, to date, few studies focus on their interaction effects on students' learning of algebra variable concepts.

Material and methods:
A mini learning system was developed to support the learning activities. A 2 × 2 factorial design was used, and 86 students were invited to participate in the experimental instruction and assigned to four groups: comparison with game-challenge, comparison, game-challenge, and control.

Results:
The results showed that (1) a significant interaction effect on the students’ algebra variable learning achievement: the comparison with game-challenge group performed significantly better than the comparison group and the game-challenge group respectively; (2) a significant interaction effect on the students’ algebra learning attitude: the comparison with game-challenge group responded significantly more positive to algebra learning than the comparison group and the game-challenge group respectively; (3) a significant interaction effect on the students’ meta-cognitive awareness: the comparison with game-challenge group reported significantly higher scores than the comparison group and the game-challenge group respectively.

Conclusions:
The combined strategy is proposed, and it could effectively enhance students’ learning achievement, learning attitude, and meta-cognitive awareness in algebra variable learning.