The "Sheltered Instruction Observation Protocol"[R] ("SIOP"[R]) is a framework for planning and delivering instruction in content areas such as science, history, and mathematics to English language learners as well as other students. The goal of "SIOP"[R] is to help teachers integrate academic language development into their lessons, allowing students to learn and practice English as it is used in the context of school, including the vocabulary used in textbooks and lectures in each academic discipline. Using this planning framework, teachers modify the way they teach so that the language they use to explain concepts and information is comprehensible to these students. "SIOP"[R] is intended to be applicable at levels of education from pre-K through community college. The "SIOP"[R] model consists of instructional strategies that cover eight aspects of lesson design and delivery: lesson preparation, building background, comprehensible input, strategies, interaction, practice and application, lesson delivery, and review and assessment. The instructional strategies address the academic and linguistics needs of English language learners. In most cases, teachers receive professional development on the "SIOP"[R] model before using it to modify their lessons. This review of "SIOP"[R] focuses on research that examines its impact on the learning of English language learners in grades K-8. The What Works Clearinghouse (WWC) identified 32 studies of "SIOP"[R] for English language learners that were published or released between 1983 and 2012. Seven studies are within the scope of the English Language Learners review protocol but do not meet WWC evidence standards. Four studies did not establish that the comparison group was comparable to the intervention group prior to the start of the intervention. Three of these used a quasi-experimental design, and the other was a randomized controlled trial with high attrition. Three studies include only one unit--for example, school--in one condition, which makes it impossible to attribute the observed effect solely to "SIOP"[R]. Twenty-two studies are out of the scope of the English Language Learners review protocol because they have an ineligible study design. A glossary of terms is included. (Contains 2 endnotes and 2 additional sources.)