There can be little doubt that one of the main reasons for the present interest in the study of the varieties of English and their implications for language teaching is the way in which these varieties impinge on one another. Mixed populations from different ethnic sources, geographical areas, and language backgrounds find their representations in and out of the classroom. Studies of the effects of language varieties in the classroom (especially of Australian Aboriginal children) are being carried out in association with the Mount Lawley Language Center in Western Australia. These studies show that in the classrooms where different language varieties are found, students often do not respond to the teacher's control, directions, or questions. It is necessary to study whole interactions to see whether delayed communication acts are not random lapses, but part of an alternative communication strategy on the part of the children who use them. Teachers and all others in "intervariety" situations require as full and detailed an awareness as possible of the features, the communication conventions, and the cultural assumptions of the particular variety of English which they themselves use and of the language varieties with which they are most likely to be dealing. Teachers thus aware of the effects of varieties, and with a range of appropriate skills from which to choose will be able to build in their students from the earliest stages of language learning a similar sensitivity toward their own and other varieties of English. (HOD)