The purpose of this study was to examine (1) the extent to which student drug use and related measures vary among American secondary schools, and (2) how substance use varies among schools by certain school characteristics. Data come from the Monitoring the Future project's annual surveys of nationally representative samples of 8th-, 10th-, and 12th-grade students from 1991 to 2002. The results show that the preponderance of variance in drug use and related variables lies within schools; only a relatively small amount of variance is between schools. Although the variance lies primarily within schools, there remain important school-to-school differences in the extent to which students are exposed to drug use. The analyses of school characteristics show that schools do indeed differ in drug use by their students, particularly by school type, socioeconomic status, and race/ethnicity. Eighth and 10th grade (but not 12th grade) students in public schools are more likely to be cigarette smokers than students in private schools. Students in public middle schools are at higher risk for use of alcohol and marijuana; however, among 12th graders, students in Catholic schools are at higher risk. School size is generally unrelated to substance use, with few exceptions. For the most part, there is a negative association between school socioeconomic status and student substance use among 8th graders; but by 12th grade, the association tends to be positive or not significant. Racial/ethnic composition is significantly associated with student substance use, with majority African American schools typically showing the lowest rates of use at all grades.