Research suggests that adaptivity with arithmetic problem solving can be developed by placing more focus on developing students’ understanding of the underlying numerical characteristics and connections during problem solving. For this reason, the present study aimed to explore how primary school students’ game performance using the “Number Navigation Game” (NNG) game-based learning environment was related to their development of adaptive number knowledge. NNG provides extensive opportunities for working strategically with various number patterns and number–operation combinations. Sixth grade students ( N = 23) played NNG in pairs, once a week, for 7 weeks during math class. Students completed measures of adaptive number knowledge and arithmetic fl uency during preand post-testing. Results show that students’ game performance had a unique contribution to explaining students’ adaptive number knowledge during post-test. This suggests that NNG is a promising game-based learning environment for developing adaptivity with arithmetic problem solving by enhancing students’ adaptive number knowledge.