This study aimed to identify personal best goal and self-regulation as predictors of mathematics achievement for primary students. The sample comprised 3,821 (2,021 males and 1,800 females) students between Grades 3 to Grade 5 at 26 primary schools in Hong Kong. Students' personal best goals and self-regulation were used to predict their mathematics achievement six months later. Multilevel structural equation models were fitted to the data using the MPLUS software. Results showed that after controlling for student gender and grade level, students' personal best goal predicted their subsequent mathematics achievement. In contrast, self-regulation had no direct effect on students' mathematics achievement. Self-regulation affected mathematics achievement only indirectly via students' personal best goals.