The present study explored the direct influences of contextual social support, including parental involvement, perceived teacher support, and peer influence, on 11th-grade students' math achievement. The study also examined the indirect influences of these contextual social support factors on students' achievement through their math motivation in math courses. The first follow-up year data of High School Longitudinal Study of 2012 (HSLS: 09) was used for this study. Structural equation modeling (SEM) served as the main statistical technique to examine the relationships among variables. The results of this study showed three sets of important findings. The first set showed that students' perception of teacher support and peer influence were significantly and directly related to students' math achievement, with the relationship between peer influence and math achievement being positive and the relationship between perceived teacher support and math achievement being negative. Controlling for other variables in the model, parental involvement was not significantly related to student math achievement. The second set of findings demonstrated that math motivation indeed plays a significant role in mediating the relationships of social support (from teachers and peers, but not from parental involvement) and student math achievement in high school. The third set of findings indicated that both family SES and prior math achievement influenced student social support and math achievement. Furthermore, two main deviations were found between White/Asian and African-American/Hispanic student models. Perceived teacher support negatively and significantly influenced White/Asian students' math achievement, but it had no significant influence on African-American/Hispanic students. In addition, math motivation had a stronger influence on the math achievement for White/Asian students than African-American/Hispanic students. The present study makes significant theoretical and practical contributions to the body of knowledge on the role of parental involvement, perceived teacher support, and peer influence on math achievement at the high school level using nationally representative data. / PHD / The current study investigated how parental involvement, student perception of teacher support, and peer influence relate to high school students’ math achievement. In addition, this study examined whether or not math motivation acts as a mediator in the relationships between social contextual factors and math achievement. last, this study examined whether all constructs and relationships used in the study vary across White/Asian students (higher-achieving group) and African-American/Hispanic students (lower achieving group). The current study found that peer influence had a positive influence on students’ math achievement directly and indirectly through motivation. This relationship suggests that students who have peers with higher grades and higher educational aspirations are more likely to be high-achieving themselves. In addition, this study found that students’ perception of teacher support was significantly related to students’ math achievement, but surprisingly, this effect was negative and small, after controlling for other variables in the model. After a closer examination, this study found that for those students who had a lower motivation level in learning math, perceived teacher support was positively related to math achievement. By contrast, for those students at the medium and higher motivation levels, the relationship between perceived teacher support and math achievement was negative. Although perceived teacher support did not influence student math achievement directly, it supported the mediation hypothesis that motivation plays an essential role in the relationship between perceived teacher support and students’ math achievement. This pattern suggests that receiving high quality support from teachers does not automatically translate into better math achievement for high school students, but perceived teacher support encourages them to demonstrate higher levels of math motivation, which in turn contributes to their improved math achievement. Overall, this study highlighted the important effects of teachers and peers during adolescence. Therefore, it contributes important knowledge for educators and policy makers to develop early interventions, create strategies and policies, and allocate recourses to improve the success in math and narrow the achievement gap.