This study examined the associations among grit, achievement goal orientations, and mathematics achievement among Grade 10 students in a private high school in Quanzhou, Fujian Province, China. A total of 256 students participated in the study, and 248 valid responses were included in the analysis. Grit was measured through perseverance of effort and consistency of interests. Achievement goal orientations included mastery goals, performance approach goals, and performance avoidance goals. Mathematics achievement was assessed using students’ formal school test scores. Multiple regression analysis and hierarchical multiple regression analysis were conducted to examine the relationships among the variables. The results showed that perseverance of effort positively predicted all three achievement goal orientations and mathematics achievement. Consistency of interests positively predicted performance approach and performance avoidance goals, but it did not significantly predict mastery goals or mathematics achievement. Mastery goals had a significant positive relationship with mathematics achievement, whereas performance approach and performance avoidance goals did not show significant direct relationships with mathematics achievement. The decrease in the regression coefficient of perseverance of effort after mastery goals were added suggested a possible indirect role of mastery goals. These findings indicate that continued effort and mastery focused motivation are important for mathematics learning. Private high schools should support students in maintaining effort, setting clear learning goals, and responding positively to academic difficulties.