All of the students, both black and white, in three ninth-grade English classes in rural southwest Virginia were taped reading a specified passage. They then wrote at least one page in response to questions and completed the Gates-MacGinitie Reading Test. The tapes and writing samples were analyzed for the presence of specified phonological and grammatical features. Results indicated that the students utilized distinct and identifiable dialect features in their oral reading and in their writing. Higher use of grammatical features of dialect by both black and white students, and of phonological features of dialect by black students, was associated with lower reading comprehension. Such dialect interference was greater for black than for white students. In general, dialect features utilized in oral reading were more indicative of dialect interference than were those utilized in writing. (Author/AA)