The instructional programs educators design to help English Learner (EL) students work toward English proficiency look different in schools across the United States. This is due in part to the variety of approaches K-12 educators take to important questions such as: Should the program foster bilingualism or focus solely on English? Should ELs learn alongside their English-proficient peers or be taught in a tailored EL-only class? And how should English as a Second Language (ESL) specialists and general education teachers work together to make sure ELs get the support they need? At a time when policymakers, advocates, parents, and other community members are encouraged to work with schools to close achievement gaps between ELs and non-ELs, this guide aims to help these stakeholders understand the differences between EL program models. It describes the characteristics of some of the most common program types--dual language, transitional bilingual education, and English only--and examines the factors that shape schools' decisions to use a particular model or set of models. Critical analysis of the design and implementation of a school's EL instructional model is an important step in school-improvement efforts that aim to boost EL outcomes and ensure an equitable education for all.