Slim chances: A case-control study to identify factors preceding school suspension and expulsion in a nationally representative sample of adolescents

School suspension and expulsion are commonly used punishments for adolescent deviance that may perpetuate disadvantage, such as lower adult socioeceonomic status and worse health.  The risk factors for suspension and expulsion include expected factors such as adolescent deviance and lower socioeconomic status, but risk factors are only partially understood.  One cross-sectional study in NHANES-3 (1988-1994) found that low cholesterol predicted suspension among school-aged children.  This study is a case-control study to identify factors preceding incident school suspension and expulsion.  Our sample comprises respondents in the Add Health data never suspended (n=8097) or expelled (n=10603) at baseline.  We identified potential predictors of incident suspension or expulsion using survey-weighted Wald tests. To avoid false significance due to multiple comparisons, multivariate regressions used only factors that predicted both suspension and expulsion. Multivariate logistic regression controlled for gender, race, age, and test scores. Among students never suspended or expelled, 4.7% were suspended and 0.007% were expelled in the next year.  Risk factors for both first suspension and expulsion in bivariate analysis included lower BMI, male gender, Black race, lower standardized test scores, higher depression scores; lifetime use of marijuana, cocaine, inhalants, and any illegal drugs; and more friends who use marijuana.  No dietary factors predicted both first suspension and expulsion.  Factors predicting greater chances of first suspension in multivariate analysis included lower BMI (OR 0.99 (0.99, 1.00), p=0.04), higher depression scores (OR 1.07 (1.04, 1.09), p<0.001); lifetime use of marijuana (3.04 (2.18, 4.23), p<0.001), cocaine (2.34 (1.32, 4.14), p<0.001), inhalants (1.92 (1.22, 3.01), p=0.005), and any illegal drugs (3.75 (2.48, 5.66), p<0.001); and more friends who use marijuana (1.61 (1.38, 1.87), p<0.001).   Depression and substance use are well-established risk factors for school suspension. Lower BMI as a risk factor for school suspension is surprising due to its association with socioeconomic status.  We would expect lower BMI to be protective, so finding the opposite increases the chances that this effect is not attributable to confounding by socioeconomic status, but it concurs with the NHANES finding.