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