The English Language Proficiency Standards (ELPS) program was developed to address the need to effectively integrate second language acquisition with quality content area instruction. English language learners (ELLs) have struggled on standardized tests and there has been little empirical evidence regarding the impact of the ELPS program on student achievement. This mixed methods case study determined the efficacy of the ELPS program for ELL students in mathematics achievement at a South Texas elementary school. The theoretical framework was based on Krashen's theory of cognitive development. Data were collected through state assessment results, teacher interviews, and teacher lesson plans. Math ELL student achievement scores in Grades 3 through 6 were compared to the assessment results of students in the same grades throughout Texas. "T" tests were used to compare standardized test results. While 55% of ELLs passed the Texas Assessment of Knowledge and Skills (TAKS) mathematics test, they were behind their non-ELL peers ("t" (4) = -3.060; p = 0.055). Lesson plans and interviews of elementary teachers of ELL students helped determine the actual use of the ELPS program. A line-by-line qualitative analysis of participants' responses was conducted to reveal themes regarding program efficacy. Although ELPS was adopted in the Texas school system, a review of the data indicated that ELPS has yet to be fully integrated into the curriculum. ELLs are still struggling but have closed some of the achievement gaps in mathematics. If teachers fully implement ELPS through careful planning and appropriate adaptations, they might better guide instruction and increase positive academic outcomes for ELL students, resulting in positive social change. [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.]