The purpose of this study was to investigate the effect of the Sheltered Instruction Observation Protocol (SIOP) strategies upon English language learners' (ELLs) self-efficacy and academic performance in the mathematics classroom. Being able to face academic challenges, while maintaining a high level of motivation and enjoyment in mathematics is a strong precursor of students' academic mathematical achievement. Therefore, it is essential that educators are utilizing effective instructional strategies that positively impact students' math self-efficacy. This research study explored the extent to which the SIOP strategies impacted ELL feelings of motivation, enjoyment, values, and security about learning mathematics. This study also measured the effect of the SIOP strategies on ELL mathematical performance. A quantitative, quasi-experimental research design was chosen to address the effect of the SIOP strategies on students' math self-efficacy and math academic achievement. The SIOP strategies had a positive impact in ELL levels of enjoyment, security, and motivation in the mathematics classroom as well as their math academic achievement. For this reason, educators should employ the SIOP strategies to address ELL mathematical academic performance, self-efficacy, and overall perception of themselves as learners. To accomplish this, a systematic approach to capacity building and resource allocation needs to take place at the federal, state, and local school levels to assist educators in creating and implementing effective lesson plans, instructional activities, and assessments rooted in the SIOP strategies. This approach will ultimately impact students' math self-efficacy and academic growth. [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://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]