The self-report questionnaire was anonymously administered to a stratified probability sample of 4,306 school students in grades 5, 7, 9, 11, and 13. Consistency of drug use was more apparent in the school grades with greater prevalence rates of drug use. Drug use was unevenly distributed and was localized within a relatively small proportion of all schools and geographical areas covered. Among the 17 categories of substances studied, the least frequently used substances were most localized. The study shows a general absence of misrepresentation of drug use by students, which corroborates findings reported by other researchers who have indicated that the problems of reliability and validity of self-reported drug use appear to be more related to difficulties in recalling and self-defining drug use than to its deliberate misrepresentation. The study suggests that data on self-reported student drug use, as found in this and similar surveys, can be accepted with reasonable confidence. 1 table, 40 references. (Author abstract modified)