To obtain nationally representative estimates of the prevalence of secondhand smoke (SHS) exposure at U.S. schools, we assessed the prevalence and correlates of SHS exposure at school among U.S. middle and high school students using data from the 2011 National Youth Tobacco Survey comprising of 18,866 students spread across all the U.S. states. Overall prevalence of SHS exposure at school was 25.7% (95% CI: [23.6%, 27.8%]). Multivariate logistic regression indicated that having =1 smoker friends (adjusted Odds Ratio [aOR] = 2.92; p < 0.001); being a smoker (aOR = 2.75; p < 0.001); and being aged 13-16 years, or =17 years (vs. 9-12 years) significantly increased the likelihood of SHS exposure. Understanding the health risks of SHS exposure alone did not seem to play a significant role in reducing exposure (aOR = 0.89; p = 0.342). These findings show there are significant levels of SHS exposure among students at U.S. middle and high schools, and sustained multipronged efforts are needed to reduce youth SHS exposure.