Whereas it is often a challenge to keep students motivated and interested in academic tasks, it is more of a challenge to have students stay motivated and interested in academic tasks outside school during nonschool hours—homework. Prior research, however, has largely overlooked the reasons or purposes students have for doing homework and their interest in homework. Informed by achievement goal theory and interest theory, along with cultural differences pertaining to these theories, the present study uses reciprocal models to study longitudinal relationships among homework goal orientation, interest, and math achievement. Participants were 1450 Chinese students in grade 8. Results found reciprocal influences of mastery-approach and math achievement. Additionally, prior mastery-approach had a positive effect on subsequent performance-approach. Furthermore, prior interest had a positive effect on subsequent mastery-approach. Meanwhile, prior performance-approach negatively influenced subsequent achievement. Taken together, the present study points to the complex interplay among mastery-approach, performance-approach, homework interest, and math achievement over time. These findings hold important practical implications (e.g., to promote mastery-approach and math achievement simultaneously and to help students focus on developing competencies through math homework, not how well they have done compared with their peers).