The fundamental principles underlying the "No Child Left Behind" (NCLB) Act of 2001" focus on high standards of learning and instruction with the goal of increasing academic achievement--reading and math in particular--within all identified subgroups in the K-12 population. One of these subgroups is the growing population of English Language Learners (ELLs). NCLB has increased awareness of the academic needs and achievement of ELLs as schools, districts, and states are held accountable for teaching English and content knowledge to this special and heterogeneous group of learners. However, ELLs present a unique set of challenges to educators because of the central role played by academic language proficiency in the acquisition and assessment of content-area knowledge. Educators have raised multiple questions about effective practices and programs to support the academic achievement of all ELLs, including questions about classroom instruction and targeted interventions in reading and math, the special needs of adolescent newcomers, and the inclusion of ELLs in large-scale assessments. While ELLs vary in their academic outcomes and many thrive in U.S. schools, there is indeed a significant proportion--whether or not formally designated Limited English Proficient (LEP) or English Language Learner (ELL) and thus receiving support services for language development--who struggle considerably in developing English proficiency and academic skills, as well as meeting grade-level standards. This document was written primarily with this latter group in mind, and, in particular, the group of ELLs who are adolescent newcomers. This group of ELLs has a relatively short period of time in which to simultaneously develop academic language skills and master grade-level content. This document provides evidence-based recommendations for policymakers, administrators, and teachers in middle and high schools who seek to make informed decisions about effectively serving adolescent newcomers. (Contains 42 endnotes.) [For related reports, see "Research-Based Recommendations for Instruction and Academic Interventions. Practical Guidelines for the Education of English Language Learners. Book 1 of 3" (ED517790) and "Research-Based Recommendations for the Use of Accommodations in Large-Scale Assessments. Practical Guidelines for the Education of English Language Learners. Book 3 of 3" (ED517792).]