Today's K-12 American classrooms are rich with students from families of diverse cultural, socioeconomic, and linguistic backgrounds. An increasingly important dimension of diversity in contemporary schools is language and, in particular, the relative proficiency students have in English and other languages when they enter school, whether at the primary, elementary, or secondary level. Language is the key to academic success because it provides access to the curriculum. In schools within the United States, that key is English. In this chapter, the authors discuss programs and approaches for educating students who come to school with limited proficiency in English.