This study aims to explore longitudinal associations among homework expectancy, mastery-approach, homework effort, and mathematics achievement involving middle school students over one school year. Results indicated that there was support for a positive reciprocal influence of mastery-approach and effort; greater initial mastery-approach resulted in greater later effort, and higher initial effort resulted in higher later mastery-approach. Results further indicated that higher initial mastery-approach led to higher later expectancy and achievement. Furthermore, the latent expectancy × mastery-approach interaction showed a significant effect on subsequent achievement; mastery-approach exerted a more positive effect on subsequent achievement when aligned with higher expectancy.