The authors examined the relationships among teacher classroom practices, student motivation, and mathematics achievement in high school. The data for this study was drawn from the base-year data of High School Longitudinal Study of 2009. Structural equation modeling method was used to estimate the relationships among variables. The results indicate that conceptual teaching positively affected student mathematics achievement, whereas procedural emphasis in mathematics instruction had a negative effect. Teacher support influenced student mathematics achievement indirectly through students' mathematics self-efficacy, and also influenced students' interest in mathematics courses. Finally, students with higher levels of family socioeconomic status and prior achievement were more likely to have teachers who use conceptual teaching strategies. Students with higher prior achievement were also more likely to perceive higher levels of teacher support. The findings have theoretical and practical implications.