Bilingual education means that equal emphasis is given to the development of the child's first language and to the learning of English as a second language. The teacher should know exactly where his students are in the development of their first language when they begin to study the second language. This requires a knowledge of the language acquisition process. By using language patterns from the student's own linguistic inventory to present content material in the classroom, the teacher increases the chances of successful communication. Using the child's dialect of the first language is also important if his classroom experiences are to be nontraumatic. When enough information on the acquisition of the first language is gathered, guidelines can be established as to what language structures are developmentally characteristic for children of different age levels, thereby enabling teachers to help students who may be losing fluency in their mother tongue. Knowledge about first language acquisition helps the teacher of English avoid those structures that the student cannot yet grasp in his first language. More research is needed on the varieties of the first language spoken in given geographic areas. A detailed summary of the author's research on the acquisition of Spanish by Mexican-American children in South Texas is included. (PM)