Promoting problem-solving and reasoning among all U.S. students and closing mathematics achievement gaps across different racial groups have become important foci in the current U.S. mathematics education reform. Framed through three contentious theoretical assumptions underlying reformed teaching, traditional teaching, and culturally relevant pedagogy, this dissertation investigates the relationship between the two kinds of teaching and the relevant mathematics achievements of students across racial/ethnic groups. The study examines specifically such a relationship drawing on U.S. eighth grade data set from the Trend in International Mathematics and Science Study (TIMSS) 2007 and using a two-level hierarchical linear modeling (HLM) approach. Results from the study indicated that reformed teaching is positively and significantly related to Caucasian, African-American, and Hispanic students' overall mathematics achievement, problem-solving and basic skills achievement, but is not related to Asian-American students' three mathematics performance measures. In addition, this study found that the traditional teaching approach is also positively and significantly related to Caucasian and Hispanic students' overall mathematics achievement, problem-solving and basic skills achievement, but is not related to African-American and Asian-American students' three mathematics performance measures. Results from this study help support the theoretical assumptions in culturally relevant pedagogy and pose challenges to the assumptions underlying reform-minded and traditional instructions about the impacts of different teaching approaches on the mathematics performance of students across different racial/ethnic groups. Implications for how to improve teaching and teacher education practices and future directions of research were also discussed.