The present study explores the potential of gameplay performance to predict gains in adaptive expertise among primary school students. More specifically, this research evaluates adaptive number knowledge (ANK), an ability to understand whole-number relations and apply this knowledge flexibly to solve new problems. Our study involved 130 primary school students playing the digital game “Seven Spells”, which focuses on arithmetic operations and numeric tables. Students’ ANK skills were assessed through a pen-and-paper timed task before and after playing the game for six weeks. Three gameplay performance metrics were collected: the highest level achieved in a multi-player mode, the highest score in single-player mode, and the leaderboard position in single-player mode. Linear regression analysis revealed that the progress against virtual opponents significantly predicted various improvements in ANK skills. Conversely, higher leaderboard positions in the single-player mode were unexpectedly correlated with some reduced ANK gains, likely due to a lack of engagement in this game mode. Student feedback indicated a preference for multiplayer mode, which may have fostered higher engagement and skill development. Our contribution suggests games can support adaptive expertise development and highlights the importance of identifying specific game design features for learning.