Curiosity and interest are often viewed as closely related constructs in psychology. This study examined Taiwanese 4th and 8th grade students’ mathematics performance on problems varying in difficulty and their individual and situational interests in mathematics. Despite Taiwan’s consistently high international performance rankings, Taiwanese students generally report low interest in mathematics. Using a quantitative-method design involving 137 fourth graders and 131 eighth graders from northern Taiwan, the study assessed students’ mathematics performance, individual interest and situational interest experienced during problem-solving. The results indicated that students in both grades performed significantly better on low-difficulty problems compared to high-difficulty problems. Additionally, fourth graders demonstrated significantly higher individual and situational interest than eighth graders. Specifically, fourth graders reported higher situational interest in low-difficulty problems compared to high-difficulty problems, whereas eighth graders showed no significant difference. Correlational analyses revealed significant positive relationships between mathematics performance and interest. For fourth graders, high-difficulty problem performance correlated strongly with both individual and situational interest, whereas no significant correlation was found for low-difficulty problems. Conversely, eighth graders exhibited consistent positive correlations between performance and interest across both high- and low-difficulty problems. Furthermore, fourth graders’ situational interest during problem-solving tasks was significantly higher than their general individual interest, a distinction not observed among eighth graders. The study contributes to understanding the complex dynamics between mathematics problem difficulty, performance, and interest, emphasizing the critical role educational practices and curriculum design play in supporting students’ long-term engagement in mathematics learning.