This quantitative study examined teachers' self-efficacy in teaching multilingual learners (MLL) and implementing the Sheltered Instruction Observation Protocol (SIOP) to support MLL instruction in classrooms. The problem is that teachers' self-efficacy when teaching MLLs may affect them not utilizing the best research-based Tier 1 instructional practices, such as those outlined in the SIOP, to support MLLs' instruction in the classrooms. Two research questions guided the study: RQ1: Is there a direct correlation between teachers' self-efficacy in teaching MLLs and teachers' implementation of SIOP in classrooms? and RQ2: What influences contribute to teachers' self-efficacy in teaching MLLs and implementing SIOP in the classrooms? Although 20 participants began the Qualtrics survey, only 17 completed the survey. Of these, 76.5% (n = 13) were female, and 23.5% (n = 4) were male. Spearman's correlation examined the relationship between teachers' self-efficacy in teaching MLLs and SIOP implementation. The results showed correlations between teachers' self-efficacy and their implementation of the SIOP model. When teachers are exposed to proven practices and understand how to apply the skill set in the classrooms, their MLLs will have academic success. [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.]