This study examines how large scale assessments like the Scholastic Aptitude Test (SAT), developed for students proficient in academic English, may not produce reliable and valid outcomes for academically vulnerable students, namely English Language Learners (ELLs). This mixed-methods study was conducted to uncover differences between the old and new mathematics sections of the SAT, to see if differences in mathematical performance correlate to language abilities by looking at students' approach, and to explore teacher perceptions, attitudes, and pedagogical practice in the instruction of English learners. The study took place in a New Jersey school district. Seventy-eight students of varying language proficiencies were administered an old and new SAT--Mathematics (SAT-M) section. After scores were statistically analyzed, fifteen students were purposefully chosen to be interviewed. For a more comprehensive view of scores, students were asked to think out loud as they completed selected test items and answer questions pertaining to their background, problem-solving methodology, misconceptions, and limitations. Similarly, nine teachers were given a survey and the exams to pinpoint difficult questions, explain why students struggle, identify what English learners' needs are, and describe how the needs are met. Qualitative data revealed that students' performance was a reflection of mathematical and/or language challenges, or lack of exposure to certain mathematical concepts. Additionally, test structure and time constraints had confounding effects on student performance. Even though a variety of cognitive processes were observed, they seemed more aligned to a student's academic track rather than linguistic abilities. With ELLs usually consigned to lower track mathematics classes, the interconnectedness of class, language, and expectations remains critical. Teachers' responses reveal their pessimism in overcoming students' language access barrier and low sense of mathematical efficacy. Teachers' efforts to provide a more equitable education to ELLs reveal tensions between reform curriculum and equity. Findings of this study contribute to the discussion on factors that may lead to the marginalization of ELLs on national assessments. The results have important implications for test construction and challenges the conceptualization of what "language" is and what being "college and career" ready means. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]