Employing data from the first (2009) and second (2011) waves of the High School Longitudinal Study of 2009 (HSLS:09), this dissertation examines the relationship between mathematical literacy practices and U.S. Latina/os’ high school achievement. Additionally, this work investigates whether such relationship is influenced by students’ English-language background. HSLS:09 consists of nationally representative quantitative data from high school students as well as their families, teachers, classrooms and schools. Using an opportunity-to-learn conceptual framework, relationships between Latina/o students’ language, literacy and mathematics data are analyzed using a quasi-experimental design (QED) that incorporates principal components analysis, propensity score matching and multi-level linear regression techniques. This study proposes a quantitative operationalization of mathematical literacy practices and contributes insights about the relationship between content-area knowledge, instructional practices and language acquisition. Results inform policy and practice sequentially by providing evidence of the relationship between mathematical literacy practices in secondary mathematics and Latina/os’ mathematics achievement.