English language learners (ELLs) at a south Florida elementary school have consistently struggled with the mathematics segment of the Florida Comprehensive Assessment Test. Examining the relationship between ELLs' mathematics scores and English proficiency might provide local educators with ideas for reversing a downward trend in ELLs' mathematics performance. Krashen's theory of comprehensible input as a precursor to second language proficiency formed the theoretical framework for this quantitative, correlational study. The study investigates the predictive power of English proficiency on mathematics scores, controlling for gender, socioeconomic status (SES), and grade level among ELLs at the south Florida elementary school. English proficiency, gender, SES, and grade level comprised the predictor variables, with mathematics scores as the criterion variable. Multiple linear regression was used in analyzing archival data for 177 ELLs in Grades 3 to 5. English proficiency emerged as a statistically significant predictor of mathematics scores. Coefficients revealed that mathematics scores increased simultaneously with English proficiency but inversely with grade level. Grade level moderated the influence of English proficiency on mathematics scores, but gender and SES had no significant moderating influence. Factors other than English proficiency might influence ELLs' decreasing mathematics achievement and warrant further research. This study might encourage educators to develop mathematics assessments commensurate with English proficiency levels within grade. The outcome might reverse the downward trend in mathematics achievement while enhancing ELLs' opportunities for social mobility. [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/en-US/products/dissertations/individuals.shtml.]