Introduction:
Private settings are major sources of secondhand smoke (SHS) exposure among youth. We measured youth exposures to home and vehicle SHS, and investigated effect of exposure on academic performance.

Methods:
The 2016 National Youth Tobacco Survey of US 6th-12th graders was analyzed (n=20,675). Exposure was a report of having breathed SHS in a vehicle and in the home within the past 7 days. Primary outcome was grade repetition, measured with a surrogate indicator ‘Later-Age-Than-Expected for grade’ (LATE)—defined as being older than peers in the same grade based on age-grade placement standards. Being over-aged relative to peers within the same grade level could be indicative of either delayed school entry, or having repeated the same or earlier grade levels ≥1 time—both of which are associated with poor academic performance. Descriptive and multivariable analyses were performed among all students and never tobacco users.

Results:
Among all students, past-7-day SHS exposures were: vehicle (21.4%, 5.56 million); home (21.7%, 5.64 million); vehicle or home (29.0%, 7.50 million); vehicle and home (14.0%, 3.63 million). Prevalence of past 7-day home or vehicle SHS exposure was: tobacco-free households, 6.5%; households with combustible-only users, 42.9%; households with smokeless tobacco/e-cigarette-only users, 15.3%; and households with combined tobacco products usage, 60.1%. Among never tobacco product users, odds of LATE were higher among those exposed to SHS in car/home non-daily (AOR=1.62; 95%CI=1.13-2.31) and daily (AOR=1.95; 95%CI=1.22-3.13) than unexposed.

Conclusions:
Academic performance was associated with SHS exposure. Smoke-free environments, including homes/cars, are critical to protect youth from SHS exposure.