Recent developments in education policy in the USA have focused attention on language and literacy, especially for bilingual learners, in US schools. More specifically, these efforts, prominently related to the implementation of the Common Core State Standards (CCSS), focus on the development of "academic English" for immigrant students. The focus on language in school contexts has renewed interest in the classic Basic Interpersonal Communication Skills (BICS)/Cognitive Academic Language Proficiency (CALP) distinction. The article reviews the BICS/CALP distinction in relation to other dichotomies of language proficiency, and promotes an alternative view of language development in school for bilingual children known as second language instructional competence, or SLIC. While SLIC has seemed useful to many in the field, there is a need for further theoretical development of the concept, with attention to how SLIC, rather than the BICS/CALP dichotomy, might usefully guide effective teaching for second language learners in US schools. A theory of language in school, in relation to monolingual and bilingual speakers with developing second language proficiency, is proposed, drawing on recent work in language minority education and second language acquisition.