Today's teachers need access to a wide range of information to function in the classroom. They need a thorough understanding of how language figures in education, and for that reason they must receive systematic and intensive preparation in educational linguistics. A thorough grounding in linguistics would support teachers' undertakings overall, and in particular in teaching literacy skills and working with English language learners. If approached coherently, such preparation would also cover many of the desired teacher competencies, relating to skills in assessing children, in individualizing instruction, and in respecting diversity. This paper lays out a rationale for why current and prospective teachers need to know more about language, and what specific sorts of knowledge they need. Requisite knowledge about oral language, oral language used in formal and academic contexts, and written language is discussed. In the final section, courses are suggested that teacher preparation programs should offer to teacher candidates. This course list may also be seen as specifying aspects of an integrated, in-depth professional development program for inservice teachers. A glossary is appended. (Contains 53 references.) (KFT)